# Aristotelian physics

Aristotelian physics is a form of natural science described in the works of the Greek philosopher Aristotle (384–322 BCE). In his work Physics, Aristotle intended to establish general principles of change that govern all natural bodies, both living and inanimate, celestial and terrestrial – including all motion (change with respect to place), quantitative change (change with respect to size or number), qualitative change, and substantial change ("coming to be" (coming into existence, "generation") or "passing away" (no longer existing, "corruption")).

To Aristotle, "physics" was a broad field that included subjects such as the philosophy of mind, sensory experience, memory, anatomy and biology. It constitutes the foundation of the thought underlying many of his works.

## Methods

A page from an 1837 edition of the ancient Greek philosopher Aristotle's Physica, a book addressing a variety of subjects including the philosophy of nature and topics now part of its modern-day namesake: physics.

nature is everywhere the cause of order.[1]

— Aristotle, Physics VIII.1

While consistent with common human experience, Aristotle's principles were not based on controlled, quantitative experiments, so they do not describe our universe in the precise, quantitative way now expected of science. Contemporaries of Aristotle like Aristarchus rejected these principles in favor of heliocentrism, but their ideas were not widely accepted. Aristotle's principles were difficult to disprove merely through casual everyday observation, but later development of the scientific method challenged his views with experiments and careful measurement, using increasingly advanced technology such as the telescope and vacuum pump.

In claiming novelty for their doctrines, those natural philosophers who developed the “new science” of the seventeenth century frequently contrasted “Aristotelian” physics with their own. Physics of the former sort, so they claimed, emphasized the qualitative at the expense of the quantitative, neglected mathematics and its proper role in physics (particularly in the analysis of local motion), and relied on such suspect explanatory principles as final causes and “occult” essences. Yet in his Physics Aristotle characterizes physics or the “science of nature” as pertaining to magnitudes (megethê), motion (or “process” or “gradual change” – kinêsis), and time (chronon) (Phys III.4 202b30–1). Indeed, the Physics is largely concerned with an analysis of motion, particularly local motion, and the other concepts that Aristotle believes are requisite to that analysis.[2]

— Michael J. White, "Aristotle on the Infinite, Space, and Time" in Blackwell Companion to Aristotle

There are clear differences between modern and Aristotelian physics, the main being the use of mathematics, largely absent in Aristotle. Some recent studies, however, have re-evaluated Aristotle's physics, stressing both its empirical validity and its continuity with modern physics.[3]

## Concepts

Peter Apian's 1524 representation of the universe, heavily influenced by Aristotle's ideas. The terrestrial spheres of water and earth (shown in the form of continents and oceans) are at the center of the universe, immediately surrounded by the spheres of air, and then fire, where meteorites and comets were believed to originate. The surrounding celestial spheres from inner to outer are those of the Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn, each indicated by a planet symbol. The eighth sphere is the firmament of fixed stars, which include the visible constellations. The precession of the equinoxes caused a gap between the visible and notional divisions of the zodiac, so medieval Christian astronomers created a ninth sphere, the Crystallinum which holds an unchanging version of the zodiac.[4][5] The tenth sphere is that of the divine prime mover proposed by Aristotle (though each sphere would have an unmoved mover). Above that, Christian theology placed the "Empire of God".
What this diagram does not show is how Aristotle explained the complicated curves that the planets make in the sky. To preserve the principle of perfect circular motion, he proposed that each planet was moved by several nested spheres, with the poles of each connected to the next outermost, but with axes of rotation offset from each other. Though Aristotle left the number of spheres open to empirical determination, he proposed adding to the many-sphere models of previous astronomers, resulting in a total of 44 or 55 celestial spheres.

### Elements and spheres

Aristotle divided his universe into "terrestrial spheres" which were "corruptible" and where humans lived, and moving but otherwise unchanging celestial spheres.

Aristotle believed that four classical elements make up everything in the terrestrial spheres:[6] earth, air, fire and water.[a][7] He also held that the heavens are made of a special weightless and incorruptible (i.e. unchangeable) fifth element called "aether".[7] Aether also has the name "quintessence", meaning, literally, "fifth being".[8]

Aristotle considered heavy substances such as iron and other metals to consist primarily of the element earth, with a smaller amount of the other three terrestrial elements. Other, lighter objects, he believed, have less earth, relative to the other three elements in their composition.[8]

The four classical elements were not invented by Aristotle; they were originated by Empedocles. During the Scientific Revolution, the ancient theory of classical elements was found to be incorrect, and was replaced by the empirically tested concept of chemical elements.

#### Celestial spheres

According to Aristotle, the Sun, Moon, planets and stars – are embedded in perfectly concentric "crystal spheres" that rotate eternally at fixed rates. Because the celestial spheres are incapable of any change except rotation, the terrestrial sphere of fire must account for the heat, starlight and occasional meteorites.[9] The lowest, lunar sphere is the only celestial sphere that actually comes in contact with the sublunary orb's changeable, terrestrial matter, dragging the rarefied fire and air along underneath as it rotates.[10] Like Homer's æthere (αἰθήρ) – the "pure air" of Mount Olympus – was the divine counterpart of the air breathed by mortal beings (άήρ, aer). The celestial spheres are composed of the special element aether, eternal and unchanging, the sole capability of which is a uniform circular motion at a given rate (relative to the diurnal motion of the outermost sphere of fixed stars).

The concentric, aetherial, cheek-by-jowl "crystal spheres" that carry the Sun, Moon and stars move eternally with unchanging circular motion. Spheres are embedded within spheres to account for the "wandering stars" (i.e. the planets, which, in comparison with the Sun, Moon and stars, appear to move erratically). Mercury, Venus, Mars, Jupiter, and Saturn are the only planets (including minor planets) which were visible before the invention of the telescope, which is why Neptune and Uranus are not included, nor are any asteroids. Later, the belief that all spheres are concentric was forsaken in favor of Ptolemy's deferent and epicycle model. Aristotle submits to the calculations of astronomers regarding the total number of spheres and various accounts give a number in the neighborhood of fifty spheres. An unmoved mover is assumed for each sphere, including a "prime mover" for the sphere of fixed stars. The unmoved movers do not push the spheres (nor could they, being immaterial and dimensionless) but are the final cause of the spheres' motion, i.e. they explain it in a way that's similar to the explanation "the soul is moved by beauty".

### Terrestrial change

The four terrestrial elements

Unlike the eternal and unchanging celestial aether, each of the four terrestrial elements are capable of changing into either of the two elements they share a property with: e.g. the cold and wet (water) can transform into the hot and wet (air) or the cold and dry (earth) and any apparent change into the hot and dry (fire) is actually a two-step process. These properties are predicated of an actual substance relative to the work it is able to do; that of heating or chilling and of desiccating or moistening. The four elements exist only with regard to this capacity and relative to some potential work. The celestial element is eternal and unchanging, so only the four terrestrial elements account for "coming to be" and "passing away" – or, in the terms of Aristotle's De Generatione et Corruptione (Περὶ γενέσεως καὶ φθορᾶς), "generation" and "corruption".

### Natural place

The Aristotelian explanation of gravity is that all bodies move toward their natural place. For the elements earth and water, that place is the center of the (geocentric) universe;[11] the natural place of water is a concentric shell around the earth because earth is heavier; it sinks in water. The natural place of air is likewise a concentric shell surrounding that of water; bubbles rise in water. Finally, the natural place of fire is higher than that of air but below the innermost celestial sphere (carrying the Moon).

In Book Delta of his Physics (IV.5), Aristotle defines topos (place) in terms of two bodies, one of which contains the other: a "place" is where the inner surface of the former (the containing body) touches the outer surface of the other (the contained body). This definition remained dominant until the beginning of the 17th century, even though it had been questioned and debated by philosophers since antiquity.[12] The most significant early critique was made in terms of geometry by the 11th-century Arab polymath al-Hasan Ibn al-Haytham (Alhazen) in his Discourse on Place.[13]

### Natural motion

Terrestrial objects rise or fall, to a greater or lesser extent, according to the ratio of the four elements of which they are composed. For example, earth, the heaviest element, and water, fall toward the center of the cosmos; hence the Earth and for the most part its oceans, will have already come to rest there. At the opposite extreme, the lightest elements, air and especially fire, rise up and away from the center.[14]

The elements are not proper substances in Aristotelian theory (or the modern sense of the word). Instead, they are abstractions used to explain the varying natures and behaviors of actual materials in terms of ratios between them.

Motion and change are closely related in Aristotelian physics. Motion, according to Aristotle, involved a change from potentiality to actuality.[15] He gave example of four types of change, namely change in substance, in quality, in quantity and in place.[16]

Aristotle's laws of motion. In Physics he states that objects fall at a speed proportional to their weight and inversely proportional to the density of the fluid they are immersed in. This is a correct approximation for objects in Earth's gravitational field moving in air or water.[3]

Aristotle proposed that the speed at which two identically shaped objects sink or fall is directly proportional to their weights and inversely proportional to the density of the medium through which they move.[17] While describing their terminal velocity, Aristotle must stipulate that there would be no limit at which to compare the speed of atoms falling through a vacuum, (they could move indefinitely fast because there would be no particular place for them to come to rest in the void). Now however it is understood that at any time prior to achieving terminal velocity in a relatively resistance-free medium like air, two such objects are expected to have nearly identical speeds because both are experiencing a force of gravity proportional to their masses and have thus been accelerating at nearly the same rate. This became especially apparent from the eighteenth century when partial vacuum experiments began to be made, but some two hundred years earlier Galileo had already demonstrated that objects of different weights reach the ground in similar times.[18]

### Unnatural motion

Apart from the natural tendency of terrestrial exhalations to rise and objects to fall, unnatural or forced motion from side to side results from the turbulent collision and sliding of the objects as well as transmutation between the elements (On Generation and Corruption).

#### Chance

In his Physics Aristotle examines accidents (συμβεβηκός, symbebekòs) that have no cause but chance. "Nor is there any definite cause for an accident, but only chance (τύχη, týche), namely an indefinite (ἀόριστον, "aóriston") cause" (Metaphysics V, 1025a25).

It is obvious that there are principles and causes which are generable and destructible apart from the actual processes of generation and destruction; for if this is not true, everything will be of necessity: that is, if there must necessarily be some cause, other than accidental, of that which is generated and destroyed. Will this be, or not? Yes, if this happens; otherwise not (Metaphysics VI, 1027a29).

### Continuum and vacuum

Aristotle argues against the indivisibles of Democritus (which differ considerably from the historical and the modern use of the term "atom"). As a place without anything existing at or within it, Aristotle argued against the possibility of a vacuum or void. Because he believed that the speed of an object's motion is proportional to the force being applied (or, in the case of natural motion, the object's weight) and inversely proportional to the density of the medium, he reasoned that objects moving in a void would move indefinitely fast – and thus any and all objects surrounding the void would immediately fill it. The void, therefore, could never form.[19]

The "voids" of modern-day astronomy (such as the Local Void adjacent to our own galaxy) have the opposite effect: ultimately, bodies off-center are ejected from the void due to the gravity of the material outside.[20]

### Four causes

According to Aristotle, there are four ways to explain the aitia or causes of change. He writes that "we do not have knowledge of a thing until we have grasped its why, that is to say, its cause."[21][22]

Aristotle held that there were four kinds of causes.[22][23]

#### Material

The material cause of a thing is that of which it is made. For a table, that might be wood; for a statue, that might be bronze or marble.

“In one way we say that the aition is that out of which. as existing, something comes to be, like the bronze for the statue, the silver for the phial, and their genera” (194b2 3—6). By “genera,” Aristotle means more general ways of classifying the matter (e.g. “metal”; “material”); and that will become important. A little later on. he broadens the range of the material cause to include letters (of syllables), fire and the other elements (of physical bodies), parts (of wholes), and even premisses (of conclusions: Aristotle re-iterates this claim, in slightly different terms, in An. Post II. 11).[24]

— R.J. Hankinson, "The Theory of the Physics" in Blackwell Companion to Aristotle

#### Formal

The formal cause of a thing is the essential property that makes it the kind of thing it is. In Metaphysics Book Α Aristotle emphasizes that form is closely related to essence and definition. He says for example that the ratio 2:1, and number in general, is the cause of the octave.

"Another [cause] is the form and the exemplar: this is the formula (logos) of the essence (to ti en einai), and its genera, for instance the ratio 2:1 of the octave” (Phys 11.3 194b26—8)... Form is not just shape... We are asking (and this is the connection with essence, particularly in its canonical Aristotelian formulation) what it is to be some thing. And it is a feature of musical harmonics (first noted and wondered at by the Pythagoreans) that intervals of this type do indeed exhibit this ratio in some form in the instruments used to create them (the length of pipes, of strings, etc.). In some sense, the ratio explains what all the intervals have in common, why they turn out the same.[25]

— R.J. Hankinson, "Cause" in Blackwell Companion to Aristotle

#### Efficient

The efficient cause of a thing is the primary agency by which its matter took its form. For example, the efficient cause of a baby is a parent of the same species and that of a table is a carpenter, who knows the form of the table. In his Physics II, 194b29—32, Aristotle writes: "there is that which is the primary originator of the change and of its cessation, such as the deliberator who is responsible [sc. for the action] and the father of the child, and in general the producer of the thing produced and the changer of the thing changed".

Aristotle’s examples here are instructive: one case of mental and one of physical causation, followed by a perfectly general characterization. But they conceal (or at any rate fail to make patent) a crucial feature of Aristotle’s concept of efficient causation, and one which serves to distinguish it from most modern homonyms. For Aristotle, any process requires a constantly operative efficient cause as long as it continues. This commitment appears most starkly to modern eyes in Aristotle’s discussion of projectile motion: what keeps the projectile moving after it leaves the hand? “Impetus,” “momentum,” much less “inertia,” are not possible answers. There must be a mover, distinct (at least in some sense) from the thing moved, which is exercising its motive capacity at every moment of the projectile’s flight (see Phys VIII. 10 266b29—267a11). Similarly, in every case of animal generation, there is always some thing responsible for the continuity of that generation, although it may do so by way of some intervening instrument (Phys II.3 194b35—195a3).[25]

— R.J. Hankinson, "Causes" in Blackwell Companion to Aristotle

#### Final

The final cause is that for the sake of which something takes place, its aim or teleological purpose: for a germinating seed, it is the adult plant,[26] for a ball at the top of a ramp, it is coming to rest at the bottom, for an eye, it is seeing, for a knife, it is cutting.

Goals have an explanatory function: that is a commonplace, at least in the context of action-ascriptions. Less of a commonplace is the view espoused by Aristotle, that finality and purpose are to be found throughout nature, which is for him the realm of those things which contain within themselves principles of movement and rest (i.e. efficient causes); thus it makes sense to attribute purposes not only to natural things themselves, but also to their parts: the parts of a natural whole exist for the sake of the whole. As Aristotle himself notes, “for the sake of” locutions are ambiguous: "A is for the sake of B" may mean that A exists or is undertaken in order to bring B about; or it may mean that A is for B’s benefit (An II.4 415b2—3, 20—1); but both types of finality have, he thinks, a crucial role to play in natural, as well as deliberative, contexts. Thus a man may exercise for the sake of his health: and so “health,” and not just the hope of achieving it, is the cause of his action (this distinction is not trivial). But the eyelids are for the sake of the eye (to protect it: PA II.1 3) and the eye for the sake of the animal as a whole (to help it function properly: cf. An II.7).[27]

— R.J. Hankinson, "Causes" in Blackwell Companion to Aristotle

### Biology

According to Aristotle, the science of living things proceeds by gathering observations about each natural kind of animal, organizing them into genera and species (the differentiae in History of Animals) and then going on to study the causes (in Parts of Animals and Generation of Animals, his three main biological works).[28]

The four causes of animal generation can be summarized as follows. The mother and father represent the material and efficient causes, respectively. The mother provides the matter out of which the embryo is formed, while the father provides the agency that informs that material and triggers its development. The formal cause is the definition of the animal’s substantial being (GA I.1 715a4: ho logos tês ousias). The final cause is the adult form, which is the end for the sake of which development takes place.[28]

— Devin M. Henry, "Generation of Animals" in Blackwell Companion to Aristotle

#### Organism and mechanism

The four elements make up the uniform materials such as blood, flesh and bone, which are themselves the matter out of which are created the non-uniform organs of the body (e.g. the heart, liver and hands) "which in turn, as parts, are matter for the functioning body as a whole (PA II. 1 646a 13—24)".[24]

[There] is a certain obvious conceptual economy about the view that in natural processes naturally constituted things simply seek to realize in full actuality the potentials contained within them (indeed, this is what is for them to be natural); on the other hand, as the detractors of Aristotelianism from the seventeenth century on were not slow to point out, this economy is won at the expense of any serious empirical content. Mechanism, at least as practiced by Aristotle’s contemporaries and predecessors, may have been explanatorily inadequate — but at least it was an attempt at a general account given in reductive terms of the lawlike connections between things. Simply introducing what later reductionists were to scoff at as “occult qualities” does not explain — it merely, in the manner of Molière’s famous satirical joke, serves to re-describe the effect. Formal talk, or so it is said, is vacuous.

Things are not however quite as bleak as this. For one thing, there’s no point in trying to engage in reductionist science if you don’t have the wherewithal, empirical and conceptual, to do so successfully: science shouldn't be simply unsubstantiated speculative metaphysics. But more than that, there is a point to describing the world in such teleologically loaded terms: it makes sense of things in a way that atomist speculations do not. And further, Aristotle’s talk of species-forms is not as empty as his opponents would insinuate. He doesn't simply say that things do what they do because that's the sort of thing they do: the whole point of his classificatory biology, most clearly exemplified in PA, is to show what sorts of function go with what, which presuppose which and which are subservient to which. And in this sense, formal or functional biology is susceptible of a type of reductionism. We start, he tells us, with the basic animal kinds which we all pre-theoretically (although not indefeasibly) recognize (cf. PA I.4): but we then go on to show how their parts relate to one another: why it is, for instance, that only blooded creatures have lungs, and how certain structures in one species are analogous or homologous to those in another (such as scales in fish, feathers in birds, hair in mammals). And the answers, for Aristotle, are to be found in the economy of functions, and how they all contribute to the overall well-being (the final cause in this sense) of the animal.[29]

— R.J. Hankinson, "The Relations between the Causes" in Blackwell Companion to Aristotle

#### Psychology

According to Aristotle, perception and thought are similar, though not exactly alike in that perception is concerned only with the external objects that are acting on our sense organs at any given time, whereas we can think about anything we choose. Thought is about universal forms, in so far as they've been successfully understood, based on our memory of having encountered instances of those forms directly.[30]

Aristotle’s theory of cognition rests on two central pillars: his account of perception and his account of thought. Together, they make up a significant portion of his psychological writings, and his discussion of other mental states depends critically on them. These two activities, moreover, are conceived of in an analogous manner, at least with regard to their most basic forms. Each activity is triggered by its object – each, that is, is about the very thing that brings it about. This simple causal account explains the reliability of cognition: perception and thought are, in effect, transducers, bringing information about the world into our cognitive systems, because, at least in their most basic forms, they are infallibly about the causes that bring them about (An III.4 429a13–18). Other, more complex mental states are far from infallible. But they are still tethered to the world, in so far as they rest on the unambiguous and direct contact perception and thought enjoy with their objects.[30]

— Victor Caston, "Phantasia and Thought" in Blackwell Companion To Aristotle

## Medieval commentary

The Aristotelian theory of motion came under criticism and modification during the Middle Ages. Modifications began with John Philoponus in the 6th century, who partly accepted Aristotle's theory that "continuation of motion depends on continued action of a force" but modified it to include his idea that a hurled body also acquires an inclination (or "motive power") for movement away from whatever caused it to move, an inclination that secures its continued motion. This impressed virtue would be temporary and self-expending, meaning that all motion would tend toward the form of Aristotle's natural motion.

In The Book of Healing (1027), the 11th-century Persian polymath Avicenna developed Philoponean theory into the first coherent alternative to Aristotelian theory. Inclinations in the Avicennan theory of motion were not self-consuming but permanent forces whose effects were dissipated only as a result of external agents such as air resistance, making him "the first to conceive such a permanent type of impressed virtue for non-natural motion". Such a self-motion (mayl) is "almost the opposite of the Aristotelian conception of violent motion of the projectile type, and it is rather reminiscent of the principle of inertia, i.e. Newton's first law of motion."[31]

The eldest Banū Mūsā brother, Ja'far Muhammad ibn Mūsā ibn Shākir (800-873), wrote the Astral Motion and The Force of Attraction. The Persian physicist, Ibn al-Haytham (965-1039) discussed the theory of attraction between bodies. It seems that he was aware of the magnitude of acceleration due to gravity and he discovered that the heavenly bodies "were accountable to the laws of physics".[32] The Persian polymath Abū Rayhān al-Bīrūnī (973-1048) was the first to realize that acceleration is connected with non-uniform motion (as later expressed by Newton's second law of motion).[33] During his debate with Avicenna, al-Biruni also criticized the Aristotelian theory of gravity firstly for denying the existence of levity or gravity in the celestial spheres; and, secondly, for its notion of circular motion being an innate property of the heavenly bodies.[34]

In 1121, al-Khazini, in The Book of the Balance of Wisdom, proposed that the gravity and gravitational potential energy of a body varies depending on its distance from the centre of the Earth.[35] Hibat Allah Abu'l-Barakat al-Baghdaadi (1080–1165) wrote al-Mu'tabar, a critique of Aristotelian physics where he negated Aristotle's idea that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, a fundamental law of classical mechanics and an early foreshadowing of Newton's second law of motion.[36] Like Newton, he described acceleration as the rate of change of speed.[37]

In the 14th century, Jean Buridan developed the theory of impetus as an alternative to the Aristotelian theory of motion. The theory of impetus was a precursor to the concepts of inertia and momentum in classical mechanics.[38] Buridan and Albert of Saxony also refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus.[39] In the 16th century, Al-Birjandi discussed the possibility of the Earth's rotation and, in his analysis of what might occur if the Earth were rotating, developed a hypothesis similar to Galileo's notion of "circular inertia".[40] He described it in terms of the following observational test:

"The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba). And this perpendicular is away from the tangent point of the Earth’s sphere and the plane of the perceived (hissi) horizon. This point moves with the motion of the Earth and thus there will be no difference in place of fall of the two rocks."[41]

## Life and death of Aristotelian physics

Aristotle depicted by Rembrandt, 1653

The reign of Aristotelian physics, the earliest known speculative theory of physics, lasted almost two millennia. After the work of many pioneers such as Copernicus, Tycho Brahe, Galileo, Descartes and Newton, it became generally accepted that Aristotelian physics was neither correct nor viable.[8] Despite this, it survived as a scholastic pursuit well into the seventeenth century, until universities amended their curricula.

In Europe, Aristotle's theory was first convincingly discredited by Galileo's studies. Using a telescope, Galileo observed that the Moon was not entirely smooth, but had craters and mountains, contradicting the Aristotelian idea of the incorruptibly perfect smooth Moon. Galileo also criticized this notion theoretically; a perfectly smooth Moon would reflect light unevenly like a shiny billiard ball, so that the edges of the moon's disk would have a different brightness than the point where a tangent plane reflects sunlight directly to the eye. A rough moon reflects in all directions equally, leading to a disk of approximately equal brightness which is what is observed.[42] Galileo also observed that Jupiter has moons – i.e. objects revolving around a body other than the Earth – and noted the phases of Venus, which demonstrated that Venus (and, by implication, Mercury) traveled around the Sun, not the Earth.

According to legend, Galileo dropped balls of various densities from the Tower of Pisa and found that lighter and heavier ones fell at almost the same speed. His experiments actually took place using balls rolling down inclined planes, a form of falling sufficiently slow to be measured without advanced instruments.

In a relatively dense medium such as water, a heavier body falls faster than a lighter one. This led Aristotle to speculate that the rate of falling is proportional to the weight and inversely proportional to the density of the medium. From his experience with objects falling in water, he concluded that water is approximately ten times denser than air. By weighing a volume of compressed air, Galileo showed that this overestimates the density of air by a factor of forty.[43] From his experiments with inclined planes, he concluded that if friction is neglected, all bodies fall at the same rate (which is also not true, since not only friction but also density of the medium relative to density of the bodies has to be negligible. Aristotle correctly noticed that medium density is a factor but focused on body weight instead of density. Galileo neglected medium density which led him to correct conclusion for vacuum).

Galileo also advanced a theoretical argument to support his conclusion. He asked if two bodies of different weights and different rates of fall are tied by a string, does the combined system fall faster because it is now more massive, or does the lighter body in its slower fall hold back the heavier body? The only convincing answer is neither: all the systems fall at the same rate.[42]

Followers of Aristotle were aware that the motion of falling bodies was not uniform, but picked up speed with time. Since time is an abstract quantity, the peripatetics postulated that the speed was proportional to the distance. Galileo established experimentally that the speed is proportional to the time, but he also gave a theoretical argument that the speed could not possibly be proportional to the distance. In modern terms, if the rate of fall is proportional to the distance, the differential expression for the distance y travelled after time t is:

${\displaystyle {dy \over dt}\propto y}$

with the condition that ${\displaystyle y(0)=0}$. Galileo demonstrated that this system would stay at ${\displaystyle y=0}$ for all time. If a perturbation set the system into motion somehow, the object would pick up speed exponentially in time, not quadratically.[43]

Standing on the surface of the Moon in 1971, David Scott famously repeated Galileo's experiment by dropping a feather and a hammer from each hand at the same time. In the absence of a substantial atmosphere, the two objects fell and hit the Moon's surface at the same time.[44]

The first convincing mathematical theory of gravity – in which two masses are attracted toward each other by a force whose effect decreases according to the inverse square of the distance between them – was Newton's law of universal gravitation. This, in turn, was replaced by the General theory of relativity due to Albert Einstein.

## Modern evaluations of Aristotle's physics

Modern scholars differ in their opinions of whether Aristotle's physics were sufficiently based on empirical observations to qualify as science, or else whether they were derived primarily from philosophical speculation and thus fail to satisfy the scientific method.[45]

One scholar has argued that Aristotle's physics are an accurate and non-intuitive representation of a particular domain (motion in fluids), and thus are just as scientific as Newton's laws of motion, which also are accurate in some domains while failing in others (i.e. special and general relativity).[45]

## As listed in the Corpus Aristotelicum

Key
Bekker
number
Work Latin name
Physics (natural philosophy)
184a Physics Physica
268a On the Heavens De Caelo
314a On Generation and Corruption De Generatione et Corruptione
338a Meteorology Meteorologica
391a On the Universe De Mundo
402a On the Soul De Anima

Parva Naturalia  ("Little Physical Treatises")
436a Sense and Sensibilia De Sensu et Sensibilibus
449b On Memory De Memoria et Reminiscentia
453b On Sleep De Somno et Vigilia
458a On Dreams De Insomniis
462b On Divination in Sleep De Divinatione per Somnum
464b On Length and Shortness
of Life
De Longitudine et Brevitate Vitae
467b On Youth, Old Age, Life
and Death, and Respiration
De Juventute et Senectute, De
Vita et Morte, De Respiratione

481a On Breath De Spiritu

486a History of Animals Historia Animalium
639a Parts of Animals De Partibus Animalium
698a Movement of Animals De Motu Animalium
704a Progression of Animals De Incessu Animalium
715a Generation of Animals De Generatione Animalium

791a On Colors De Coloribus
800a On Things Heard De audibilibus
805a Physiognomonics Physiognomonica
815a On Plants De Plantis
830a On Marvellous Things Heard De mirabilibus auscultationibus
847a Mechanics Mechanica
859a Problems* Problemata*
968a On Indivisible Lines De Lineis Insecabilibus
973a The Situations and Names
of Winds
Ventorum Situs
974a On Melissus, Xenophanes,
and Gorgias

## Notes

a ^ Here, the term "Earth" does not refer to planet Earth, known by modern science to be composed of a large number of chemical elements. Modern chemical elements are not conceptually similar to Aristotle's elements; the term "air", for instance, does not refer to breathable air.

## References

1. ^ Lang, H.S. (2007). The Order of Nature in Aristotle's Physics: Place and the Elements. Cambridge University Press. p. 290. ISBN 9780521042291.
2. ^ White, Michael J. (2009). "Aristotle on the Infinite, Space, and Time". Blackwell Companion to Aristotle. p. 260.
3. ^ a b Rovelli, Carlo (2015). "Aristotle's Physics: A Physicist's Look". Journal of the American Philosophical Association. 1 (1): 23–40. arXiv:1312.4057. doi:10.1017/apa.2014.11.
4. ^ [1]
5. ^ History of Science
6. ^ "Physics of Aristotle vs. The Physics of Galileo". Archived from the original on 11 April 2009. Retrieved 6 April 2009.
7. ^ a b "www.hep.fsu.edu" (PDF). Retrieved 26 March 2007.
8. ^ a b c "Aristotle's physics". Retrieved 6 April 2009.
9. ^ Aristotle, meteorology.
10. ^ Sorabji, R. (2005). The Philosophy of the Commentators, 200-600 AD: Physics. G - Reference, Information and Interdisciplinary Subjects Series. Cornell University Press. p. 352. ISBN 978-0-8014-8988-4. LCCN 2004063547.
11. ^ De Caelo II. 13-14.
12. ^ For instance, by Simplicius in his Corollaries on Place.
13. ^ El-Bizri, Nader (2007). "In Defence of the Sovereignty of Philosophy: al-Baghdadi's Critique of Ibn al-Haytham's Geometrisation of Place". Arabic Sciences and Philosophy. 17: 57–80. doi:10.1017/s0957423907000367.
14. ^ Tim Maudlin (2012-07-22). Philosophy of Physics: Space and Time: Space and Time (Princeton Foundations of Contemporary Philosophy) (p. 2). Princeton University Press. Kindle Edition. "The element earth's natural motion is to fall— that is, to move downward. Water also strives to move downward but with less initiative than earth: a stone will sink though water, demonstrating its overpowering natural tendency to descend. Fire naturally rises, as anyone who has watched a bonfire can attest, as does air, but with less vigor."
15. ^ Bodnar, Istvan, "Aristotle's Natural Philosophy" in The Stanford Encyclopedia of Philosophy (Spring 2012 Edition, ed. Edward N. Zalta).
16. ^ Bodnar, Istvan, "Aristotle's Natural Philosophy" in The Stanford Encyclopedia of Philosophy (Spring 2012 Edition, ed. Edward N. Zalta).
17. ^ Gindikin, S.G. (1988). Tales of Physicists and Mathematicians. Birkh. p. 29. ISBN 9780817633172. LCCN 87024971.
18. ^ Lindberg, D. (2008), The beginnings of western science: The European scientific tradition in philosophical, religious, and institutional context, prehistory to AD 1450 (2nd ed.), University of Chicago Press.
19. ^ Land, Helen, The Order of Nature in Aristotle's Physics: Place and the Elements (1998).
20. ^ Tully; Shaya; Karachentsev; Courtois; Kocevski; Rizzi; Peel (2008). "Our Peculiar Motion Away From the Local Void". The Astrophysical Journal. 676 (1): 184. arXiv:0705.4139. Bibcode:2008ApJ...676..184T. doi:10.1086/527428.
21. ^ Aristotle, Physics 194 b17–20; see also: Posterior Analytics 71 b9–11; 94 a20.
22. ^ a b "Four Causes". Falcon, Andrea. Aristotle on Causality. Stanford Encyclopedia of Philosophy 2008.
23. ^ Aristotle, "Book 5, section 1013a", Metaphysics, Hugh Tredennick (trans.) Aristotle in 23 Volumes, Vols. 17, 18, Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1933, 1989; (hosted at perseus.tufts.edu.) Aristotle also discusses the four causes in his Physics, Book B, chapter 3.
24. ^ a b Hankinson, R.J. "The Theory of the Physics". Blackwell Companion to Aristotle. p. 216.
25. ^ a b Hankinson, R.J. "Causes". Blackwell Companion to Aristotle. p. 217.
26. ^ Aristotle. Parts of Animals I.1.
27. ^ Hankinson, R.J. "Causes". Blackwell Companion to Aristotle. p. 218.
28. ^ a b Henry, Devin M. (2009). "Generation of Animals". Blackwell Companion to Aristotle. p. 368.
29. ^ Hankinson, R.J. "Causes". Blackwell Companion to Aristotle. p. 222.
30. ^ a b Caston, Victor (2009). "Phantasia and Thought". Blackwell Companion to Aristotle. pp. 322–2233.
31. ^ Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1): 477–482 [477]
32. ^ Duhem, Pierre (1908, 1969). To Save the Phenomena: An Essay on the Idea of Physical theory from Plato to Galileo, University of Chicago Press, Chicago, p. 28.
33. ^
34. ^ Rafik Berjak and Muzaffar Iqbal, "Ibn Sina--Al-Biruni correspondence", Islam & Science, June 2003.
35. ^ Mariam Rozhanskaya and I. S. Levinova (1996), "Statics", in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, vol. 2, pp. 614–642 [621-622]. (Routledge, London and New York.)
36. ^ Shlomo Pines (1970). "Abu'l-Barakāt al-Baghdādī, Hibat Allah". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 26–28. ISBN 0-684-10114-9.
(cf. Abel B. Franco (October 2003). "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4), pp. 521–546 [528].)
37. ^ A. C. Crombie, Augustine to Galileo 2, p. 67.
38. ^ Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1): 477–482
39. ^ Gutman, Oliver (2003). Pseudo-Avicenna, Liber Celi Et Mundi: A Critical Edition. Brill Publishers. p. 193. ISBN 90-04-13228-7.
40. ^ (Ragep & Al-Qushji 2001, pp. 63–4)
41. ^ (Ragep 2001, pp. 152–3)
42. ^ a b Galileo Galilei, Dialogue Concerning the Two Chief World Systems.
43. ^ a b Galileo Galilei, Two New Sciences.
44. ^ https://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html
45. ^ a b https://arxiv.org/pdf/1312.4057.pdf

## Sources

• Ragep, F. Jamil (2001). "Tusi and Copernicus: The Earth's Motion in Context". Science in Context. Cambridge University Press. 14 (1–2): 145–163. doi:10.1017/s0269889701000060.
• Ragep, F. Jamil; Al-Qushji, Ali (2001). "Freeing Astronomy from Philosophy: An Aspect of Islamic Influence on Science". Osiris, 2nd Series. 16 (Science in Theistic Contexts: Cognitive Dimensions): 49–64 and 66–71. Bibcode:2001Osir...16...49R. doi:10.1086/649338.
• H. Carteron (1965) "Does Aristotle Have a Mechanics?" in Articles on Aristotle 1. Science eds. Jonathan Barnes, Malcolm Schofield, Richard Sorabji (London: General Duckworth and Company Limited), 161-174.

• Katalin Martinás, “Aristotelian Thermodynamics” in Thermodynamics: history and philosophy: facts, trends, debates (Veszprém, Hungary 23–28 July 1990), pp. 285–303.
Abu al-Salt

Abū al‐Ṣalt Umayya ibn ʿAbd al‐ʿAzīz ibn Abī al‐Ṣalt al‐Dānī al‐Andalusī (c. 1068—October 23, 1134), known in Latin as Albuzale, was an Andalusian-Arab polymath who wrote about pharmacology, geometry, Aristotelian physics, and astronomy. His works on astronomical instruments were read both in the Islamic world and Europe. He also worked as a physician, a teacher of alchemy, and wrote treatises on medicine, philosophy, music, and history. He became well known in Europe through translations of his works made in the Iberian Peninsula and in southern France. He is also credited with introducing Andalusian music to Tunis, which later led to the development of the Tunisian ma'luf.

Ali Qushji

Ala al-Dīn Ali ibn Muhammed (1403 – 16 December 1474), known as Ali Qushji (Ottoman Turkish/Persian language: علی قوشچی, kuşçu – falconer in Turkish; Latin: Ali Kushgii) was an astronomer, mathematician and physicist originally from Samarkand, who settled in the Ottoman Empire some time before 1472. As a disciple of Ulugh Beg, he is best known for the development of astronomical physics independent from natural philosophy, and for providing empirical evidence for the Earth's rotation in his treatise, Concerning the Supposed Dependence of Astronomy upon Philosophy. In addition to his contributions to Ulugh Beg's famous work Zij-i-Sultani and to the founding of Sahn-ı Seman Medrese, one of the first centers for the study of various traditional Islamic sciences in the Ottoman caliphate, Ali Kuşçu was also the author of several scientific works and textbooks on astronomy.

Aristotelian

Aristotelian may refer to:

Aristotle (384–322 BCE), Greek philosopher

Aristotelianism, the philosophical tradition begun by Aristotle

Aristotelian ethics

Aristotelian logic, term logic

Aristotelian physics, the natural sciences

Aristotelian Society, founded at a meeting on 19 April 1880

Aristotelian theology

Aristotelian tragedy

Byzantine science

Byzantine science played an important role in the transmission of classical knowledge to the Islamic world and to Renaissance Italy, and also in the transmission of Islamic science to Renaissance Italy. Its rich historiographical tradition preserved ancient knowledge upon which splendid art, architecture, literature and technological achievements were built.

Byzantines stood behind several technological advancements.

Christopher Wren

Sir Christopher Wren PRS FRS (; 30 October 1632 [O.S. 20 October] – 8 March 1723 [O.S. 25 February]) was an English anatomist, astronomer, geometer, and mathematician-physicist, as well as one of the most highly acclaimed English architects in history.

He was accorded responsibility for rebuilding 52 churches in the City of London after the Great Fire in 1666, including what is regarded as his masterpiece, St Paul's Cathedral, on Ludgate Hill, completed in 1710.The principal creative responsibility for a number of the churches is now more commonly attributed to others in his office, especially Nicholas Hawksmoor. Other notable buildings by Wren include the Royal Naval College, Greenwich, and the south front of Hampton Court Palace. The Wren Building, the main building at the College of William and Mary, Virginia, is attributed to Wren.

Educated in Latin and Aristotelian physics at the University of Oxford, Wren was a founder of the Royal Society (president 1680–1682), and his scientific work was highly regarded by Isaac Newton and Blaise Pascal.

Cosmology in medieval Islam

Islamic cosmology is the cosmology of Islamic societies. It is mainly derived from the Qur'an, Hadith, Sunnah, and current Islamic as well as other pre-Islamic sources. The Qur'an itself mentions seven heavens.

Equant

Equant (or punctum aequans) is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of the planets. The equant is used to explain the observed speed change in planetary orbit during different stages of the orbit. This planetary concept allowed Ptolemy to keep the theory of uniform circular motion alive by stating that the path of heavenly bodies was uniform around one point and circular around another point.

Geosphere

There are several conflicting definitions for geosphere.

The geosphere may be taken as the collective name for the lithosphere, the hydrosphere, the cryosphere, and the atmosphere.In Aristotelian physics, the term was applied to four spherical natural places, concentrically nested around the center of the Earth, as described in the lectures Physica and Meteorologica. They were believed to explain the motions of the four terrestrial elements: Earth, Water, Air and Fire.

In modern texts and in Earth system science, geosphere refers to the solid parts of the Earth; it is used along with atmosphere, hydrosphere, and biosphere to describe the systems of the Earth (the interaction of these systems with the magnetosphere is sometimes listed). In that context, sometimes the term lithosphere is used instead of geosphere or solid Earth. The lithosphere, however, only refers to the uppermost layers of the solid Earth (oceanic and continental crustal rocks and uppermost mantle).Since space exploration began, it has been observed that the extent of the ionosphere or plasmasphere is highly variable, and often much larger than previously appreciated, at times extending to the boundaries of the Earth's magnetosphere or geomagnetosphere. This highly variable outer boundary of geogenic matter has been referred to as the "geopause," to suggest the relative scarcity of such matter beyond it, where the solar wind dominates.

Index of philosophy of science articles

An index list of articles about the philosophy of science.

John Hennon

John (Johannes) Hennon (died after 1484) was a Dutch medieval philosopher in the late Scholastic tradition. He was from Nijmegen, and studied at the University of Paris, where he received his magister artium and baccalaureus formatus in sacra pagina (1463).

As a student of Paris, Hennon was heavily influenced by William of Ockham and Roger Bacon. He wrote a Latin commentary on the Physics of Aristotle, the Commentarii in Aristotelis libros Physicorum, which was completed on 1 October 1473 if a seventeenth-century source is to be believed. Examining the state of science in the late Middle Ages, physicist, historian, and philosopher Pierre Duhem, in Le système du monde, isolates Hennon's account of the vacuum and a plurality of worlds.

Hennon believed that nature abhors a vacuum and therefore no natural void was possible, though God could create one. A void, however, is not defined by a positive distance between surfaces in which there is nothing, but rather as the capacity (potentialitas) for a body to be interposed between the two surfaces equal to that which is there when it is full. Hennon affirms that ice is denser than liquid water, and that a sealed vase of water will break upon freezing because nature abhors a vacuum. He believes further that two smooth plates could not be separated (again, because nature abhors a vacuum) unless there were some air still between them, which with enough force may become rarefied, allowing the plates to be separated.

Hennon is less original on a plurality of worlds, where he borrows text verbatim from Albert of Saxony's Quaestiones in libros de Caelo et Mundo. He follows Albert and John Buridan in asserting that a multiplicity of worlds is not contradictory and therefore possible through divien omnipotence. In fact, God could create an infinite multitude of beings, since Hennon finds no contradiction between infinity and magnitude. Duhem in his analysis of Hennon's chapter De Caelo et Mundo, argues that Hennon relied on the Condemnations of 1277 by Stephen Tempier to attack Aristotelian physics, and thus the position that the earth cannot move.

Liber de orbe

Liber de orbe was a Latin translation made in 1130s CE of an Arabic work attributed to the 8th century astrologer Mashallah ibn Athari.

The work's main topic is cosmology and is considered as one of the earliest works on Aristotelian physics available in Latin.

List of converts to Islam from Judaism

This is a list of notable converts to Islam from Judaism.

Hibat Allah Abu'l-Barakat al-Baghdaadi – influential 12th-century physicist, philosopher, and scientist who wrote a critique of Aristotelian philosophy and Aristotelian physics.

Ka'ab al-Ahbar - 7th-century Yemenite Jew. Considered to be the earliest authority on Isra'iliyyat and South Arabian lore.

Ibn Yahyā al-Maghribī al-Samaw'al – 12th-century mathematician and astronomer.

Muhammad Asad (Leopold Weiss) – Viennese journalist, author, and translator who visited the Hijaz in the 1930s, and became Pakistani ambassador to the United Nations.

Sultan Rafi Sharif Bey (Yale Singer) – 20th-century pioneer in the development of Islamic culture in the United States.

Youssef Darwish – labour lawyer and activist who was one of the few from the Karaite Jewish community to remain in Egypt after the creation of the state of Israel in 1948.

Tali Fahima – Israeli left-wing activist, convicted of aiding Palestinian fighters. Converted to Islam in Umm al-Fahm in June 2010.

Jemima Goldsmith – a British TV, film and documentary producer, journalist and campaigner.

Rashid-al-Din Hamadani – 13th-century Persian physician

Yaqub ibn Killis – 10th-century Egyptian vizier under the Fatimids.

Leila Mourad – Egyptian singer and actress of the 1940s and 1950s.

Lev Nussimbaum – 20th-century writer, journalist and orientalist.

Jacob Querido – 17th-century successor of the self-proclaimed Jewish Messiah Sabbatai Zevi.

Abdullah ibn Salam – 7th-century sahabi said to have been a rabbi of aristocratic stock.

Ibn Sahl of Seville – 13th-century Andalusian poet.

Harun ibn Musa – 8th-century scholar of Hadith and Qira'at, and the first compiler of the different styles of Qur'anic recitation.

Al-Ru'asi – 8th-century scholar of Arabic grammar and the founder of the Kufan school of grammar.

Mathematical physics

Mathematical physics refers to the development of mathematical methods for application to problems in physics. The Journal of Mathematical Physics defines the field as "the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories". It is a branch of applied mathematics, but deals with physical problems.

Minimum (disambiguation)

Minimum, a Latin word meaning the least or the smallest, may refer to:

Minimum (mathematics), a concept in mathematics

Minimum, Missouri, a community in the United States

Minima naturalia, a concept in Aristotelian physics

Philip of the Blessed Trinity

Philip of the Blessed Trinity (born at Malaucene, near Avignon, 1603; died at Naples, 28 February 1671) was a French Discalced Carmelite theologian and missionary.

Philosophy of physics

In philosophy, philosophy of physics deals with conceptual and interpretational issues in modern physics, and often overlaps with research done by certain kinds of theoretical physicists. Philosophy of physics can be very broadly lumped into three main areas:

The interpretations of quantum mechanics: Concerning issues, mainly, with how to formulate an adequate response to the measurement problem, and understand what the theory tells us about reality.

The nature of space and time: Are space and time substances, or purely relational? Is simultaneity conventional or just relative? Is temporal asymmetry purely reducible to thermodynamic asymmetry?

Inter-theoretic relations: the relationship between various physical theories, such as thermodynamics and statistical mechanics. This overlaps with the issue of scientific reduction.

Physics in the medieval Islamic world

The natural sciences saw various advancements during the Golden Age of Islam (from roughly the mid 8th to the mid 13th centuries), adding a number of innovations to the Transmission of the Classics (such as Aristotle, Ptolemy, Euclid, Neoplatonism).

During this period, Islamic theology was encouraging of thinkers to find knowledge, . Thinkers from this period included Al-Farabi, Abu Bishr Matta, Ibn Sina, al-Hassan Ibn al-Haytham and Ibn Bajjah.

These works and the important commentaries on them were the wellspring of science during the medieval period. They were translated into Arabic, the lingua franca of this period.

Islamic scholarship had inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further. However the Islamic world had a greater respect for knowledge gained from empirical observation, and believed that the universe is governed by a single set of laws. Their use of empirical observation led to the formation of crude forms of the scientific method.

The study of physics in the Islamic world started in Iraq and Egypt.

Fields of physics studied in this period include optics, mechanics (including statics, dynamics, kinematics and motion), and astronomy.

Sail On! Sail On!

"Sail On! Sail On!" is an alternate history short story by Philip José Farmer, first published in Startling Stories 1952. In an alternative 1492, Christopher Columbus sets out to find a shortened route to China and South-East Asia across the Atlantic, financed by Ferdinand V and Isabella I of Spain. However, in this timeline, the Earth is flat, though scientists and philosophers have doubts about its geological provenance, and an Angelo Angelli is mentioned as proving Aristotle's axiom that objects of different weights drop with different velocities (which Galileo Galilei disproved in our world).

Radio technology exists in 1492, and the shipboard operator of a telegraph is a "Friar Sparks", although the principles are described in religious terms involving angels' winglength as a substitute for radio waves and the involvement of cherubim hurling themselves across the ether to send the signal (giving rise to kilo-cherubs as a measurement of frequency, denoted as k c., and continuous wingheight, denoted as c w, both radio terms in the real world). Psychology also exists, which means that Columbus's vessels do not turn back despite growing unease and ominous warning signs. It turns out that the Americas do not exist, and that this world is a disc, not a sphere; so, like other transatlantic travellers, Columbus and his colleagues sail over the edge of the world into Earth orbit, and never return from their mission.

Richard Garfinkle's alternate history novel Celestial Matters (1996) describes a more elaborated Aristotelian physics and geocentric cosmology, although its flat Earth is dominated by the "Middle Kingdom" of China and the Greek-centred Delian League and is capable of its own version of spaceflight according to its own laws of physics.

Sublunary sphere

In Aristotelian physics and Greek astronomy, the sublunary sphere is the region of the geocentric cosmos below the Moon, consisting of the four classical elements: earth, water, air, and fire.The sublunary sphere was the realm of changing nature. Beginning with the Moon, up to the limits of the universe, everything (to classical astronomy) was permanent, regular and unchanging – the region of aether where the planets and stars are located. Only in the sublunary sphere did the powers of physics hold sway.

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