Internalism and externalism

Internalism and externalism are two opposing ways of explaining various subjects in several areas of philosophy. These include human motivation, knowledge, justification, meaning, and truth. The distinction arises in many areas of debate with similar but distinct meanings.

Internalism is the thesis that no fact about the world can provide reasons for action independently of desires and beliefs.[1] Externalism is the thesis that reasons are to be identified with objective features of the world.[1]

Moral philosophy


In contemporary moral philosophy, motivational internalism (or moral internalism) is the view that moral convictions (which are not necessarily beliefs, e.g. feelings of moral approval or disapproval) are intrinsically motivating. That is, the motivational internalist believes that there is an internal, necessary connection between one's conviction that X ought to be done and one's motivation to do X. Conversely, the motivational externalist (or moral externalist) claims that there is no necessary internal connection between moral convictions and moral motives.[2] That is, there is no necessary connection between the conviction that X is wrong and the motivational drive not to do X. (The use of these terms has roots in W.D. Falk's (1947) paper "'Ought' and Motivation"[3]).

These views in moral psychology have various implications. In particular, if motivational internalism is true, then an amoralist is unintelligible (and metaphysically impossible). An amoralist is not simply someone who is immoral, rather it is someone who knows what the moral things to do are, yet is not motivated to do them. Such an agent is unintelligible to the motivational internalist, because moral judgments about the right thing to do have built into them corresponding motivations to do those things that are judged by the agent to be the moral things to do. On the other hand, an amoralist is entirely intelligible to the motivational externalist, because the motivational externalist thinks that moral judgments about the right thing to do not necessitate some motivation to do those things that are judged to be the right thing to do; rather, an independent desire—such as the desire to do the right thing—is required (Brink, 2003[4]), (Rosati, 2006[5]).


There is also a distinction in ethics and action theory, largely made popular by Bernard Williams (1979, reprinted in 1981),[2] concerning internal and external reasons for action. An internal reason is, roughly, something that one has in light of one's own "subjective motivational set"---one's own commitments, desires (or wants), goals, etc. On the other hand, an external reason is something that one has independent of one's subjective motivational set. For example, suppose that Sally is going to drink a glass of poison, because she wants to commit suicide and believes that she can do so by drinking the poison. Sally has an internal reason to drink the poison, because she wants to commit suicide. However, one might say that she has an external reason not to drink the poison because, even though she wants to die, one ought not kill oneself no matter what—regardless of whether one wants to die.

Some philosophers embrace the existence of both kinds of reason, while others deny the existence of one or the other. For example, Bernard Williams (1981)[2] argues that there are really only internal reasons for action. Such a view is called internalism about reasons (or reasons internalism). Externalism about reasons (or reasons externalism) is the denial of reasons internalism.[6] It is the view that there are external reasons for action; that is, there are reasons for action that one can have even if the action is not part of one's subjective motivational set.

Consider the following situation. Suppose that it's against the moral law to steal from the poor, and Sasha knows this. However, Sasha doesn't desire to follow the moral law, and there is currently a poor person next to him. Is it intelligible to say that Sasha has a reason to follow the moral law right now (to not steal from the poor person next to him), even though he doesn't care to do so? The reasons externalist answers in the affirmative ("Yes, Sasha has a reason not to steal from that poor person."), since he believes that one can have reasons for action even if one does not have the relevant desire. Conversely, the reasons internalist answers the question in the negative ("No, Sasha does not have a reason not to steal from that poor person, though others might."). The reasons internalist claims that external reasons are unintelligible; one has a reason for action only if one has the relevant desire (that is, only internal reasons can be reasons for action). The reasons internalist claims the following: the moral facts are a reason for Sasha's action not to steal from the poor person next to him only if he currently wants to follow the moral law (or if not stealing from the poor person is a way to satisfy his other current goals—that is, part of what Williams calls his "subjective motivational set"). In short, the reasoning behind reasons internalism, according to Williams,[2] is that reasons for action must be able to explain one's action; and only internal reasons can do this.




Generally speaking, internalist conceptions of epistemic justification require that one’s justification for a belief be internal to the believer in some way. Two main varieties of epistemic internalism about justification are access internalism and ontological internalism. Access internalists require that a believer must have internal access to the justifier(s) of her belief p in order to be justified in believing p. For the access internalist, justification amounts to something like the believer being aware (or capable of being aware) of certain facts that make her belief in p rational, or her being able to give reasons for her belief in p. At minimum, access internalism requires that the believer have some kind of reflective access or awareness to whatever justifies her belief. Ontological internalism is the view that justification for a belief is established by one’s mental states. Ontological internalism can be distinct from access internalism, but the two are often thought to go together since we are generally considered to be capable of having reflective access to mental states.[7]

One popular argument for internalism is known as the 'new evil demon problem'. The new evil demon problem indirectly supports internalism by challenging externalist views of justification, particularly reliabilism. The argument asks us to imagine a subject with beliefs and experiences identical to ours, but the subject is being systematically deceived by a malicious Cartesian demon so that all their beliefs turn out false. In spite of the subject's unfortunate deception, the argument goes, we do not think this subject ceases to be rational in taking things to be as they appear as we do. After all, it is possible that we could be radically deceived in the same way, yet we are still justified in holding most of our beliefs in spite of this possibility. Since reliabilism maintains that one's beliefs are justified via reliable belief-forming processes (where reliable means yielding true beliefs), the subject in the evil demon scenario would not likely have any justified beliefs according to reliabilism because all of their beliefs would be false. Since this result is supposed to clash with our intuitions that the subject is justified in their beliefs in spite of being systematically deceived, some take the new evil demon problem as a reason for rejecting externalist views of justification.[8]


Externalist views of justification emerged in epistemology during the late 20th century. Externalist conceptions of justification assert that facts external to the believer can serve as the justification for a belief. According to the externalist, a believer need not have any internal access or cognitive grasp of any reasons or facts which make her belief justified.[9] The externalist’s assessment of justification can be contrasted with access internalism, which demands that the believer have internal reflective access to reasons or facts which corroborate their belief in order to be justified in holding it. Externalism, on the other hand, maintains that the justification for someone’s belief can come from facts that are entirely external to the agent’s subjective awareness.[7]

Alvin Goldman, one of the most well-known proponents of externalism in epistemology, is known for developing a popular form of externalism called reliabilism. In his paper, “What is Justified Belief?” Goldman characterizes the reliabilist conception of justification as such:

"If S’s believing p at t results from a reliable cognitive belief-forming process (or set of processes), then S’s belief in p at t is justified.[10]

Goldman notes that a reliable belief-forming process is one which generally produces true beliefs.[10]

A unique consequence of reliabilism (and other forms of externalism) is that one can have a justified belief without knowing one is justified (this is not possible under most forms of epistemic internalism). In addition, we do not yet know which cognitive processes are in fact reliable, so anyone who embraces reliabilism must concede that we do not always know whether some of our beliefs are justified (even though there is a fact of the matter).[10]

As a response to skepticism

In responding to skepticism, Hilary Putnam (1982[11]) claims that semantic externalism yields "an argument we can give that shows we are not brains in a vat (BIV). (See also DeRose, 1999.[12]) If semantic externalism is true, then the meaning of a word or sentence is not wholly determined by what individuals think those words mean. For example, semantic externalists maintain that the word "water" referred to the substance whose chemical composition is H2O even before scientists had discovered that chemical composition. The fact that the substance out in the world we were calling "water" actually had that composition at least partially determined the meaning of the word. One way to use this in a response to skepticism is to apply the same strategy to the terms used in a skeptical argument in the following way (DeRose, 1999[12]):

Either I am a BIV, or I am not a BIV.

If I am not a BIV, then when I say "I am not a BIV", it is true.
If I am a BIV, then, when I say "I am not a BIV", it is true (because "brain" and "vat" would only pick out the brains and vats being simulated, not real brains and real vats).
My utterance of "I am not a BIV" is true.

To clarify how this argument is supposed to work: Imagine that there is brain in a vat, and a whole world is being simulated for it. Call the individual who is being deceived "Steve." When Steve is given an experience of walking through a park, semantic externalism allows for his thought, "I am walking through a park" to be true so long as the simulated reality is one in which he is walking through a park. Similarly, what it takes for his thought, "I am a brain in a vat," to be true is for the simulated reality to be one where he is a brain in a vat. But in the simulated reality, he is not a brain in a vat.

Apart from disputes over the success of the argument or the plausibility of the specific type of semantic externalism required for it to work, there is question as to what is gained by defeating the skeptical worry with this strategy. Skeptics can give new skeptical cases that wouldn't be subject to the same response (e.g., one where the person was very recently turned into a brain in a vat, so that their words "brain" and "vat" still pick out real brains and vats, rather than simulated ones). Further, if even brains in vats can correctly believe "I am not a brain in a vat," then the skeptic can still press us on how we know we are not in that situation (though the externalist will point out that it may be difficult for the skeptic to describe that situation).

Another attempt to use externalism to refute skepticism is done by Brueckner[13] and Warfield.[14] It involves the claim that our thoughts are about things, unlike a BIV's thoughts, which cannot be about things (DeRose, 1999[12]).


Semantic externalism comes in two varieties, depending on whether meaning is construed cognitively or linguistically. On a cognitive construal, externalism is the thesis that what concepts (or contents) are available to a thinker is determined by their environment, or their relation to their environment. On a linguistic construal, externalism is the thesis that the meaning of a word is environmentally determined. Likewise, one can construe semantic internalism in two ways, as a denial of either of these two theses.

Externalism and internalism in semantics is closely tied to the distinction in philosophy of mind concerning mental content, since the contents of one's thoughts (specifically, intentional mental states) are usually taken to be semantic objects that are truth-evaluable.

See also:

Philosophy of mind

Within the context of the philosophy of mind, externalism is the theory that the contents of at least some of one's mental states are dependent in part on their relationship to the external world or one's environment.

The traditional discussion on externalism was centered around the semantic aspect of mental content. This is by no means the only meaning of externalism now. Externalism is now a broad collection of philosophical views considering all aspects of mental content and activity. There are various forms of externalism that consider either the content or the vehicles of the mind or both. Furthermore, externalism could be limited to cognition, or it could address broader issues of consciousness.

As to the traditional discussion on semantic externalism (often dubbed content externalism), some mental states, such as believing that water is wet, and fearing that the Queen has been insulted, have contents we can capture using 'that' clauses. The content externalist often appeal to observations found as early as Hilary Putnam's seminal essay, "The Meaning of 'Meaning'," (1975).[11] Putnam stated that we can easily imagine pairs of individuals that are microphysical duplicates embedded in different surroundings who use the same words but mean different things when using them.

For example, suppose that Ike and Tina's mothers are identical twins and that Ike and Tina are raised in isolation from one another in indistinguishable environments. When Ike says, "I want my mommy," he expresses a want satisfied only if he is brought to his mommy. If we brought Tina's mommy, Ike might not notice the difference, but he doesn't get what he wants. It seems that what he wants and what he says when he says, "I want my mommy," will be different from what Tina wants and what she says she wants when she says, "I want my mommy."

Externalists say that if we assume competent speakers know what they think, and say what they think, the difference in what these two speakers mean corresponds to a difference in the thoughts of the two speakers that is not (necessarily) reflected by a difference in the internal make up of the speakers or thinkers. They urge us to move from externalism about meaning of the sort Putnam defended to externalism about contentful states of mind. The example pertains to singular terms, but has been extended to cover kind terms as well such as natural kinds (e.g., 'water') and for kinds of artifacts (e.g., 'espresso maker'). There is no general agreement amongst content externalists as to the scope of the thesis.

Philosophers now tend to distinguish between wide content (externalist mental content) and narrow content (anti-externalist mental content). Some, then, align themselves as endorsing one view of content exclusively, or both. For example, Jerry Fodor (1980[15]) argues for narrow content (although he comes to reject that view in his 1995), while David Chalmers (2002)[16] argues for a two dimensional semantics according to which the contents of mental states can have both wide and narrow content.

Critics of the view have questioned the original thought experiments saying that the lessons that Putnam and later writers such as Tyler Burge (1979,[17] 1982[18]) have urged us to draw can be resisted. Frank Jackson and John Searle, for example, have defended internalist accounts of thought content according to which the contents of our thoughts are fixed by descriptions that pick out the individuals and kinds that our thoughts intuitively pertain to the sorts of things that we take them to. In the Ike/Tina example, one might agree that Ike's thoughts pertain to Ike's mother and that Tina's thoughts pertain to Tina's but insist that this is because Ike thinks of that woman as his mother and we can capture this by saying that he thinks of her as 'the mother of the speaker'. This descriptive phrase will pick out one unique woman. Externalists claim this is implausible, as we would have to ascribe to Ike knowledge he wouldn't need to successfully think about or refer to his mother.

Critics have also claimed that content externalists are committed to epistemological absurdities. Suppose that a speaker can have the concept of water we do only if the speaker lives in a world that contains H2O. It seems this speaker could know a priori that she thinks that water is wet. This is the thesis of privileged access. It also seems that she could know on the basis of simple thought experiments that she can only think that water is wet if she lives in a world that contains water. What would prevent her from putting these together and coming to know a priori that the world contains water? If we should say that no one could possibly know whether water exists a priori, it seems either we cannot know content externalism to be true on the basis of thought experiments or we cannot know what we are thinking without first looking into the world to see what it is like.

As mentioned, content externalism (limited to the semantic aspects) is only one among many other options offered by externalism by and large.

See also:

Historiography of science

Internalism in the historiography of science claims that science is completely distinct from social influences and pure natural science can exist in any society and at any time given the intellectual capacity.[19] Imre Lakatos is a notable proponent of historiographical internalism.[20]

Externalism in the historiography of science is the view that the history of science is due to its social context – the socio-political climate and the surrounding economy determines scientific progress.[19] Thomas Kuhn is a notable proponent of historiographical externalism.[21]

See also


  1. ^ a b Giuseppina D'Oro, "Collingwood, psychologism and internalism," European Journal of Philosophy 12(2):163–177 (2004).
  2. ^ a b c d Williams, Bernard (1981) "Internal and External Reasons", in Williams's Moral Luck, Cambridge: Cambridge University Press, pp. 101–13.
  3. ^ Falk, W. D. (1947) "'Ought' and Motivation", Proceedings of the Aristotelian Society, 48: 492–510
  4. ^ Brink, David (1989) "Moral Realism and the Foundations of Ethics", New York: Cambridge University Press, Ch. 3, pp. 37–80.
  5. ^ Rosati, Connie S. (2006). "Moral Motivation", The Stanford Encyclopedia of Philosophy Edward N. Zalta (ed.).
  6. ^ Finlay, Stephen & Schroeder, Mark (2008). "Reasons for Action: Internal vs. External" (§1.1). The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.))
  7. ^ a b Sosa, Ernest, Jaegwon Kim, Jeremy Fantl, Matthew McGrath. Introduction to Part V. Epistemology. By Ernest Sosa, Jaegwon Kim, Jeremy Fantl, Matthew McGrath. Malden: Blackwell, 2008. 305-309. Print.
  8. ^ "The New Evil Demon Problem" by Clayton Littlejohn, The Internet Encyclopedia of Philosophy, ISSN 2161-0002,, today's date
  9. ^ BonJour, Laurence. “Externalist Theories of Empirical Knowledge.” Epistemology. Ed. Ernest Sosa, Jaegwon Kim, Jeremy Fantl, Matthew McGrath. Malden: Blackwell, 2008. 365. Print.
  10. ^ a b c Goldman, Alvin I. “What is Justified Belief?” Epistemology. Ed. Ernest Sosa, Jaegwon Kim, Jeremy Fantl, Matthew McGrath. Malden: Blackwell, 2008. 333-347. Print
  11. ^ a b Putnam, H. (1981): "Brains in a vat" in Reason, Truth, and History, Cambridge University Press; reprinted in DeRose and Warfield, editors (1999): Skepticism: A Contemporary Reader, Oxford UP.
  12. ^ a b c DeRose, Keith (1999) "Responding to Skepticism", Skepticism: A Contemporary Reader.
  13. ^ Brueckner, Anthony (1999), Semantic Answers to Skepticism, Oxford: Oxford University Press, pp. 43–60
  14. ^ Warfield, Ted A. Skepticism (1999, ed. with Keith DeRose, Oxford, 1999)
  15. ^ Fodor, Jerry (1980) "Methodological Solipsism Considered as a Research Strategy in Cognitive Psychology", Behavioral and Brain Sciences 3:1.
  16. ^ Chalmers, David (2002) "The Components of Content", in Chalmers (ed.) Philosophy of Mind: Classical and Contemporary Readings, Oxford: Oxford University Press.
  17. ^ Burge, Tyler (1979) "Individualism and the Mental", in French, Uehling, and Wettstein (eds.) Midwest Studies in Philosophy IV, Minneapolis: University of Minnesota Press, pp. 73–121.
  18. ^ Burge, Tyler (1982) "Other Bodies", in Woodfield, Andrew, ed., Thought and Object. New York: Oxford.
  19. ^ a b Arne Hessenbruch (ed.), Reader's Guide to the History of Science, Routledge, 2013: "Internalism versus Externalism".
  20. ^ Kostas Gavroglu, Yorgos Goudaroulis, P. Nicolacopoulos (eds.), Imre Lakatos and Theories of Scientific Change, Springer, 2012, p. 211.
  21. ^ Alexander Bird, "Kuhn and the Historiography of Science" in Alisa Bokulich and William J. Devlin (eds.), Kuhn's Structure of Scientific Revolutions: 50 Years On, Springer (2015).

Further reading

  • Brink, David (1989) "Moral Realism and the Foundations of Ethics", New York: Cambridge University Press, Ch. 3, pp. 37–80.
  • Brown, Curtis (2007) "Narrow Mental Content", The Stanford Encyclopedia of Philosophy (Spring 2007 Edition), Edward N. Zalta (ed.). (link)
  • Burge, Tyler (1979) "Individualism and the Mental", in French, Uehling, and Wettstein (eds.) Midwest Studies in Philosophy IV, Minneapolis: University of Minnesota Press, pp. 73–121.
  • Burge, Tyler (1982) "Other Bodies", in Woodfield, Andrew, ed., Thought and Object. New York: Oxford.
  • Chalmers, David (2002) "The Components of Content", in Chalmers (ed.) Philosophy of Mind: Classical and Contemporary Readings, Oxford: Oxford University Press. Preprint available online
  • Cohen, Stewart (1984) "Justification and Truth", Philosophical Studies 46, pp. 279–296.
  • DeRose, Keith (1999) "Responding to Skepticism", Skepticism: A Contemporary Reader.
  • Falk, W. D. (1947) "'Ought' and Motivation", Proceedings of the Aristotelian Society, 48: 492–510
  • Finlay, Stephen & Schroeder, Mark (2008). "Reasons for Action: Internal vs. External". The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.). (link)
  • Fodor, Jerry (1980) "Methodological Solipsism Considered as a Research Strategy in Cognitive Psychology", Behavioral and Brain Sciences 3:1.
  • Fodor, Jerry (1995) The Elm and the Expert: Mentalese and its Semantics, Cambridge: MIT Press.
  • Kornblith, Hilary (ed.) (2001) Epistemology: Internalism and Externalism, Blackwell Press.
  • Lau, Joe (2004) "Externalism About Mental Content", The Stanford Encyclopedia of Philosophy (Fall 2004 Edition), Edward N. Zalta (ed.). (link)
  • Le Morvan, Pierre (2005) "A Metaphilosophical Dilemma for Epistemic Externalism", Metaphilosophy 36(5), pp. 688–707.
  • Pappas, George (2005) "Internalist vs. Externalist Conceptions of Epistemic Justification", The Stanford Encyclopedia of Philosophy (Spring 2005 Edition), Edward N. Zalta (ed.). (link)
  • Putnam, Hilary (1975) "The Meaning of 'Meaning'", in Keith Gunderson (ed.) Language, Mind and Knowledge, Minneapolis: University of Minnesota Press, pp. 131–93 (reprinted in Putnam (1975), Mind, Language and Reality: Philosophical Papers Volume 2, Cambridge: Cambridge University Press). (link)
  • Putnam, Hilary (1982) "Brains in a Vat", in Reason, Truth, and History, Cambridge University Press. (link)
  • Rosati, Connie S. (2006). "Moral Motivation", The Stanford Encyclopedia of Philosophy Edward N. Zalta (ed.). (link)
  • Smith, Basil (2013). "Internalism and Externalism in the Philosophy of Mind and Language," 'The Internet Encyclopedia of Philosophy,' P. Saka (ed.). (link)
  • Sosa, Ernest (1991) "Reliabilism and Intellectual Virtue," in E. Sosa, Knowledge In Perspective, Cambridge Press, pp. 131–145.
  • Williams, Bernard (1981) "Internal and External Reasons", in Williams's Moral Luck, Cambridge: Cambridge University Press, pp. 101–13.

External links

Brain in a vat

In philosophy, the brain in a vat (BIV; alternately known as brain in a jar) is a scenario used in a variety of thought experiments intended to draw out certain features of human conceptions of knowledge, reality, truth, mind, consciousness, and meaning. It is an updated version of René Descartes's evil demon thought experiment originated by Gilbert Harman. Common to many science fiction stories, it outlines a scenario in which a mad scientist, machine, or other entity might remove a person's brain from the body, suspend it in a vat of life-sustaining liquid, and connect its neurons by wires to a supercomputer which would provide it with electrical impulses identical to those the brain normally receives. According to such stories, the computer would then be simulating reality (including appropriate responses to the brain's own output) and the "disembodied" brain would continue to have perfectly normal conscious experiences, such as those of a person with an embodied brain, without these being related to objects or events in the real world.

Dream argument

The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore, any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine whether it is in fact reality.


In philosophy, empiricism is a theory that states that knowledge comes only or primarily from sensory experience. It is one of several views of epistemology, the study of human knowledge, along with rationalism and skepticism. Empiricism emphasises the role of empirical evidence in the formation of ideas, rather than innate ideas or traditions. However, empiricists may argue that traditions (or customs) arise due to relations of previous sense experiences.Empiricism in the philosophy of science emphasises evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori reasoning, intuition, or revelation.

Empiricism, often used by natural scientists, says that "knowledge is based on experience" and that "knowledge is tentative and probabilistic, subject to continued revision and falsification". Empirical research, including experiments and validated measurement tools, guides the scientific method.


Evidentialism is a thesis in epistemology which states that one is justified to believe something if and only if that person has evidence which supports his or her belief. Evidentialism is therefore a thesis about which beliefs are justified and which are not.

For philosophers Richard Feldman and Earl Conee, evidentialism is the strongest argument for justification because it identifies the primary notion of epistemic justification. They argue that if a person's attitude towards a proposition fits their evidence, then their doxastic attitude for that proposition is epistemically justified. Feldman and Conee offer the following argument for evidentialism as an epistemic justification:

(EJ) Doxastic attitude D toward proposition p is epistemically justified for S at t if and only if having D toward p fits the evidence.

For Feldman and Conee a person's doxastic attitude is justified if it fits their evidence. EJ is meant to show the idea that justification is characteristically epistemic. This idea makes justification dependent on evidence.

Feldman and Conee believe that because objections to EJ have become so prominent their defense for it is appropriate. The theses that object EJ are implying that epistemic justification is dependent upon the "cognitive capacities of an individual or upon the cognitive processes or information-gatherings practices that lead to an attitude." For Feldman and Conee, EJ is in contrast to these theses; EJ contends that the epistemic justification for an attitude is only dependent upon evidence.

Evil demon

The evil demon, also known as malicious demon and evil genius, is a concept in Cartesian philosophy. In the first of his 1641 Meditations on First Philosophy, Descartes imagines that an evil demon, of "utmost power and cunning has employed all his energies in order to deceive me." This evil demon is imagined to present a complete illusion of an external world, so that Descartes can say, "I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things."

Some Cartesian scholars opine that the demon is also omnipotent, and thus capable of altering mathematics and the fundamentals of logic, though omnipotence of the evil demon would be contrary to Descartes' hypothesis, as he rebuked accusations of the evil demon having omnipotence.It is one of several methods of systematic doubt that Descartes employs in the Meditations.

Evolutionary epistemology

Evolutionary epistemology refers to three distinct topics: (1) the biological evolution of cognitive mechanisms in animals and humans, (2) a theory that knowledge itself evolves by natural selection, and (3) the study of the historical discovery of new abstract entities such as abstract number or abstract value that necessarily precede the individual acquisition and usage of such abstractions.

Experience machine

The experience machine or pleasure machine is a thought experiment put forward by philosopher Robert Nozick in his 1974 book Anarchy, State, and Utopia. It is one of the best known attempts to refute ethical hedonism, and does so by imagining a choice between everyday reality and an apparently preferable simulated reality.

If the primary thesis of hedonism is that "pleasure is the good", then any component of life that is not pleasurable does nothing directly to increase one's well-being. This is a view held by many value theorists, but most famously by some classical utilitarians. Nozick attacks the thesis by means of a thought experiment. If he can show that there is something other than pleasure that has value and thereby increases our well-being, then hedonism is defeated.

Factual relativism

Aletheic relativism argues that truth itself is relative. This form of relativism has its own particular problem, regardless of whether one is talking about truth being relative to the individual, the position or purpose of the individual, or the conceptual scheme within which the truth was revealed. This problem centers on what Mandelbaum (1962) termed the "self-excepting fallacy." Largely because of the self-excepting fallacy, few authors in the philosophy of science currently accept aletheic cognitive relativism. Factual relativism (also called epistemic relativism, epistemological relativism, alethic relativism or cognitive relativism) is a way to reason where facts used to justify any claims are understood to be relative and subjective to the perspective of those proving or falsifying the proposition.


Foundationalism concerns philosophical theories of knowledge resting upon justified belief, or some secure foundation of certainty such as a conclusion inferred from a basis of sound premises. The main rival of the foundationalist theory of justification is the coherence theory of justification, whereby a body of knowledge, not requiring a secure foundation, can be established by the interlocking strength of its components, like a puzzle solved without prior certainty that each small region was solved correctly.Identifying the alternatives as either circular reasoning or infinite regress, and thus exhibiting the regress problem, Aristotle made foundationalism his own clear choice, positing basic beliefs underpinning others. Descartes, the most famed foundationalist, discovered a foundation in the fact of his own existence and in the "clear and distinct" ideas of reason, whereas Locke found a foundation in experience. Differing foundations may reflect differing epistemological emphases—empiricists emphasizing experience, rationalists emphasizing reason—but may blend both.In the 1930s, debate over foundationalism revived. Whereas Moritz Schlick viewed scientific knowledge like a pyramid where a special class of statements does not require verification through other beliefs and serves as a foundation, Otto Neurath argued that scientific knowledge lacks an ultimate foundation and acts like a raft. In the 1950s, foundationalism fell into decline – largely due to the influence of Willard Van Orman Quine, whose ontological relativity found any belief networked to one's beliefs on all of reality, while auxiliary beliefs somewhere in the vast network are readily modified to protect desired beliefs.

Classically, foundationalism had posited infallibility of basic beliefs and deductive reasoning between beliefs—a strong foundationalism. About 1975 weak foundationalism emerged. Thus recent foundationalists have variously allowed fallible basic beliefs, and inductive reasoning between them, either by enumerative induction or by inference to the best explanation. And whereas internalists require cognitive access to justificatory means, externalists find justification without such access.


Infinitism is the view that knowledge may be justified by an infinite chain of reasons. It belongs to epistemology, the branch of philosophy that considers the possibility, nature, and means of knowledge.

Mind extension

In recent years several philosophers have broached the idea that mind should not be considered to be something which is just in the head but in various ways can be spread out onto the world.

This is a materialist rather than spiritualist notion, the mind being thought of as extending over the brain, external language and media such as charts, diaries and indeed any material substrate that can become intimately involved in our mindful actions.


Reliabilism, a category of theories in the philosophical discipline of epistemology, has been advanced as a theory both of justification and of knowledge. Process reliabilism has been used as an argument against philosophical skepticism, such as the brain in a vat thought experiment.

Process reliabilism is a form of epistemic externalism.

Semantic externalism

In the philosophy of language, semantic externalism (the opposite of semantic internalism) is the view that the meaning of a term is determined, in whole or in part, by factors external to the speaker. According to an externalist position, one can claim without contradiction that two speakers could be in exactly the same brain state at the time of an utterance, and yet mean different things by that utterance, that is, the term picks out a different extension.

Simulated reality

Simulated reality is the hypothesis that reality could be simulated—for example by quantum computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation. This is quite different from the current, technologically achievable concept of virtual reality. Virtual reality is easily distinguished from the experience of actuality; participants are never in doubt about the nature of what they experience. Simulated reality, by contrast, would be hard or impossible to separate from "true" reality. There has been much debate over this topic, ranging from philosophical discourse to practical applications in computing.

Simulation hypothesis

The simulation hypothesis or simulation theory proposes that all of reality, including the Earth and the universe, is in fact an artificial simulation, most likely a computer simulation. Some versions rely on the development of a simulated reality, a proposed technology that would seem realistic enough to convince its inhabitants the simulation was real. The hypothesis has been a central plot device of many science fiction stories and films.


Swampman is the subject of a philosophical thought experiment introduced by Donald Davidson in his 1987 paper "Knowing One's Own Mind".

The Extended Mind

"The Extended Mind" by Andy Clark and David Chalmers (1998) is a seminal work in the field of extended cognition. In this paper, Clark and Chalmers present the idea of active externalism (similar to semantic or "content" externalism), in which objects within the environment function as a part of the mind. They argue that it is arbitrary to say that the mind is contained only within the boundaries of the skull. The separation between the mind, the body, and the environment is seen as an unprincipled distinction. Because external objects play a significant role in aiding cognitive processes, the mind and the environment act as a "coupled system". This coupled system can be seen as a complete cognitive system of its own. In this manner, the mind is extended into the external world. The main criterion that Clark and Chalmers list for classifying the use of external objects during cognitive tasks as a part of an extended cognitive system is that the external objects must function with the same purpose as the internal processes.

In "The Extended Mind", a thought experiment is presented to further illustrate the environment's role in connection to the mind. The fictional characters Otto and Inga are both travelling to a museum simultaneously. Otto has Alzheimer's disease, and has written all of his directions down in a notebook to serve the function of his memory. Inga is able to recall the internal directions within her memory. In a traditional sense, Inga can be thought to have had a belief as to the location of the museum before consulting her memory. In the same manner, Otto can be said to have held a belief of the location of the museum before consulting his notebook. The argument is that the only difference existing in these two cases is that Inga's memory is being internally processed by the brain, while Otto's memory is being served by the notebook. In other words, Otto's mind has been extended to include the notebook as the source of his memory. The notebook qualifies as such because it is constantly and immediately accessible to Otto, and it is automatically endorsed by him.

Going further, the authors ask and answer their own question about the role of enculturation:

"And what about socially-extended cognition? Could my mental states be partly constituted by the states of other thinkers? We see no reason why not, in principle."They bring up the recurrent theme of the role of language:

"The major burden of the coupling between agents is carried by language ... Indeed, it is not implausible that the explosion of intellectual development in recent evolutionary time is due as much to this linguistically-enabled extension of cognition as to any independent development in our inner cognitive resources."

Twin Earth thought experiment

Twin Earth is a thought experiment by philosopher Hilary Putnam, first in his paper "Meaning and Reference" (1973), and then in his paper "The Meaning of 'Meaning'" (1975), to illustrate his argument for semantic externalism, or the view that the meanings of words are ultimately not purely psychological. The Twin Earth thought experiment was one of three, the other two being the Aluminum-Molybdenum, and the Beech-Elm cases. Since the publication of these cases, philosophers have proposed numerous variations on the experiment.

Virtue epistemology

Virtue epistemology is a contemporary philosophical approach to epistemology that stresses the importance of intellectual, and specifically epistemic virtues. A distinguishing factor of virtue theories is that they use for the evaluation of knowledge the properties of the persons who hold beliefs in addition to or instead of the properties of propositions and beliefs. Some advocates of virtue epistemology claim to more closely follow theories of virtue ethics, while others see only a looser analogy between virtue in ethics and virtue in epistemology.

Intellectual virtue has been a subject of philosophy since the work of Aristotle, but virtue epistemology is a development in the contemporary analytic tradition. It is characterized by efforts to solve problems of special concern to modern epistemology, such as justification and reliabilism, by directing attention on the knower as agent in a manner similar to the way virtue ethics focuses on moral agents rather than moral acts.

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