Natural theology, once also termed physico-theology, is a type of theology that provides arguments for the existence of God based on reason and ordinary experience of nature. This distinguishes it from revealed theology, which is based on scripture and/or religious experiences, and also from transcendental theology, which is based on a priori reasoning.
Marcus Terentius Varro (116 BC – 27 BC) established a distinction between political theology (the social functions of religion), natural theology and mythical theology. His terminology became part of the Stoic tradition and then Christianity through St. Augustine and St. Thomas Aquinas.
Natural theology is thus a type of philosophy, the object of which is explanation of the nature of the gods, or of one supreme God. For monotheistic religions, this principally involves arguments about the attributes or non-attributes of God, and especially the existence of God, using arguments that do not involve recourse to supernatural revelation.
Besides Zarathushtra's Gathas, Plato gives the earliest surviving account of a natural theology. In the Timaeus, written c. 360 BC, we read: "We must first investigate concerning [the whole Cosmos] that primary question which has to be investigated at the outset in every case, — namely, whether it has always existed, having no beginning or generation, or whether it has come into existence, having begun from some beginning." In the Laws, in answer to the question as to what arguments justify faith in the gods, Plato affirms: "One is our dogma about the soul...the other is our dogma concerning the ordering of the motion of the stars".
Marcus Terentius Varro in his (lost) Antiquitates rerum humanarum et divinarum established a distinction between three kinds of theology: civil (political) (theologia civilis), natural (physical) (theologia naturalis) and mythical (theologia mythica). The theologians of civil theology are "the people", asking how the gods relate to daily life and the state (imperial cult). The theologians of natural theology are the philosophers, asking about the nature of the gods, and the theologians of mythical theology are the poets, crafting mythology.
From the 8th century AD, the Mutazilite school of Islam, compelled to defend their principles against the orthodox Islam of their day, used philosophy for support, and were among the first to pursue a rational Islamic theology, termed Ilm-al-Kalam (scholastic theology). The teleological argument was later presented by the early Islamic philosophers Alkindus and Averroes, while Avicenna presented both the cosmological argument and the ontological argument in The Book of Healing (1027).
St. Thomas Aquinas (c.1225–1274) presented several versions of the cosmological argument in his Summa Theologica, and of the teleological argument in his Summa contra Gentiles. He presented the ontological argument, but rejected it in favor of proofs that invoke cause and effect alone. His quinque viae ("five ways") in those books attempted to prove the existence of God in different ways, including (as way #5) the goal-directed actions seen in nature.
Raymond of Sabunde's Liber Naturae Sive Creaturarum, Etc. (or Theologia Naturalis), written 1434–1436, marks an important stage in the history of natural theology.
John Ray (1627–1705) also known as John Wray, was an English naturalist, sometimes referred to as the father of English natural history. He published important works on plants, animals, and natural theology, with the objective "to illustrate the glory of God in the knowledge of the works of nature or creation".
William Derham (1657–1735) continued Ray's tradition of natural theology in two of his own works, Physico-Theology, published during 1713, and Astro-Theology, 1714. These later influenced the work of William Paley.
In An Essay on the Principle of Population, published during 1798, Thomas Malthus ended with two chapters on natural theology and population. Malthus—a devout Christian—argued that revelation would "damp the soaring wings of intellect", and thus never let "the difficulties and doubts of parts of the scripture" interfere with his work.
William Paley, an important influence on Charles Darwin, who studied theology at Christ College in Cambridge, gave a well-known rendition of the teleological argument for God. During 1802 he published Natural Theology, or Evidences of the Existence and Attributes of the Deity collected from the Appearances of Nature. In this he described the Watchmaker analogy, for which he is probably best known. However, his book, which was one of the most published books of the 19th and 20th century, presents a number of teleological and cosmological arguments for the existence of God. The book served as a template for many subsequent natural theologies during the 19th century.
Professor of chemistry and natural history, Edward Hitchcock also studied and wrote on natural theology. He attempted to unify and reconcile science and religion, emphasizing geology. His major work of this type was The Religion of Geology and its Connected Sciences (1851).
The Gifford Lectures were established by the will of Adam Lord Gifford to "promote and diffuse the study of Natural Theology in the widest sense of the term—in other words, the knowledge of God." The term natural theology as used by Gifford means theology supported by science and not dependent on the miraculous.
Debates over the applicability of teleology to scientific questions continued during the nineteenth century, as Paley's argument about design conflicted with radical new theories on the transmutation of species. In order to support the scientific ideas of the time, which explored the natural world within Paley's framework of a divine designer, Francis Henry Egerton, 8th Earl of Bridgewater, a gentleman naturalist, commissioned eight Bridgewater Treatises upon his deathbed to explore "the Power, Wisdom, and Goodness of God, as manifested in the Creation." They were published first during the years 1833 to 1840, and afterwards in Bohn's Scientific Library. The treatises are:
In response to the claim in Whewell's treatise that "We may thus, with the greatest propriety, deny to the mechanical philosophers and mathematicians of recent times any authority with regard to their views of the administration of the universe", Charles Babbage published what he termed The Ninth Bridgewater Treatise, A Fragment. As his preface states, this volume was not part of that series, but rather his own considerations of the subject. He draws on his own work on calculating engines to consider God as a divine programmer setting complex laws as the basis of what we think of as miracles, rather than miraculously producing new species by creative whim. There was also a fragmentary supplement to this, published posthumously by Thomas Hill.
The theology of the Bridgewater Treatises was often disputed, given that it assumed humans could have knowledge of God acquired by observation and reasoning without the aid of revealed knowledge.
The works are of unequal merit; several of them were esteemed as apologetic literature, but they attracted considerable criticism. One notable critic of the Bridgewater Treatises was Edgar Allan Poe, who wrote Criticism. Robert Knox, an Edinburgh surgeon and major advocate of radical morphology, referred to them as the "Bilgewater Treatises", to mock the "ultra-teleological school". Though memorable, this phrase overemphasises the influence of teleology in the series, at the expense of the idealism of the likes of Kirby and Roget.
The Bridgewater Treatises