DEISM. — Etymologically, d. (from Deus) is identical with theism (from Reis), but its philosophical and historical meaning is different. The philosophical meaning commonly given today is that already specified by Kant: the deist “admits that we... can know by simple reason the existence of an original Being, but... only as a Being that possesses every reality, though we cannot give any more precise determination of it”; the theist “asserts that reason is capable of determining its object further according to the analogy with nature, that is: as a Being containing within itself the first principle of all other things through intellect and freedom. The former therefore represents in such a being only a Cause of the world (whether through the necessity of its own nature or through freedom remains undecided), the latter an Author of the world”; and shortly afterward: “the deist believes in a God, but the theist in a living God (summam intelligentiam)” (I. Kant, Kritik der reinen Vernunft, 1st ed., Riga 1781, pp. 631–33; cf. Italian trans., 2nd ed., Bari 1925, pp. 493–94).
As a historical fact, d. does not have so definite and restricted a meaning. In general, it denotes that philosophical-religious movement of the seventeenth and eighteenth centuries, either preceding, interweaving with, or merging into the Enlightenment, which tended to eliminate every supernatural element from religion and to establish a purely natural religion. In practice it assumed various forms. At the beginning of the eighteenth century Samuel Clarke (1675–1729), an opponent of d., in A demonstration of the Being and Attributes of God (London 1705), distinguished four classes of deists: 1) Those who admit God but deny him any providence: God, an intelligent cause, having drawn the world out of chaos, left it entirely to itself. 2) Those who also admit providence, but limit it to physical events alone: God takes no interest in moral good and evil, which derive only from positive laws; there is no future life for man. 3) Those who admit providence also with regard to moral life: the moral law comes from God; but there is no immortality, and consequently no sanction in a further life. 4) Those who profess all the natural truths concerning God; admit a future life; but reject every religious authority and revelation.
The term deist appears in the sixteenth century. The Calvinist pastor M. Viret, in the Épître dédicatoire to Part 2 of the Instruction chrétienne (1564), speaks of it as “un mot tout nouveau, lequel ils (i deisti) veulent opposer à Athéisme”. Of their ideas he says: “They recognize God, but do not admit Jesus Christ. The teaching of the Apostles and Evangelists is for them pure fable and fantasy.” The use of the word spread during the seventeenth century. Until the eighteenth century, and even at the beginning of the nineteenth, theism (a term of English origin, especially popularized by Ralph Cudworth, [1617–88]) was sometimes used in the same sense.
D. first had its systematic advocates in England, where, however, at least until D. Hume and E. Gibbon, it was, both in scientific and literary importance, a movement of secondary significance. Among its principal representatives, the following deserve particular mention: J. Toland (1670–1722) and M. Tindal (1656–1733). In Christianity not mysterious (London 1696), Toland intended to demonstrate, as the work’s subtitle says, “that there is nothing in the Gospel contrary to Reason, nor above it, and that no Christian doctrine can properly be called a mystery.” Revelation is admitted, but “revelation serves only to inform us, whereas the demonstration of its object is what persuades us.” In his work (often called the Bible of d.), Christianity as old as the Creation: or the Gospel a Republication of the Religion of Nature (London 1730), Tindal sought to demonstrate that natural religion was absolutely perfect from the beginning; that revelation could add nothing to it; and that Christ restored natural religion, or the law of nature. Other notable representatives of English d. were: A. Collins (1676–1729); Th. Chubb (1679–1747); Th. Morgan (d. 1743); Lord H. Bolingbroke (H. St. John, 1678–1731), a friend of Voltaire, whom he met during his exile in France and later hosted for three years in England.
English d. derived in part from France. In France it returned in a more developed form, and was spread especially through the work of Voltaire, Rousseau, and the Encyclopedists. It experienced a revival there in the nineteenth century with Cousin and the spiritualists.
In Germany, the ideas of d. arrived both directly from England and through France, and merged into, while developing within, the broader Enlightenment movement. Its advocates included: H. Samuel Reimarus (1694–1768), known especially for the Apologie oder Schutzschrift für die vernünftigen Verehrer Gottes, published posthumously (1774–77) in part by Lessing as fragments of an anonymous work found in the library of Wolfenbüttel (in Braunschweig); M. Mendelssohn (1729–86), the most notable representative of “popular philosophy,” often mentioned by Kant; and especially G. E. Lessing (1729–81). In his most mature work, which exercised an influence not limited to his own time, Erziehung des Menschengeschlechtes (Berlin 1780), he considers the Old and New Testaments as simple historical products, not, however, arbitrary ones, but founded upon the intrinsic law of humanity’s development. They are products of its infancy and youth; it belongs to maturity to discover in their dogmas the rational truths imaginatively adumbrated in them. As regards the concept of God, Kant is a theist, although in his own manner (the existence of God cannot be demonstrated speculatively, but only from the moral law of man, as a simple practical postulate); with regard to his concept of religion, however, he must be counted among the deists.
D. as a historical phenomenon is explained chiefly by the weariness and skepticism caused by the religious struggles between Catholics and Protestants, and even more by those among Protestants themselves. This is confirmed by the fact that, while it spread in England, France, and Germany, it elicited only a weak response both in Italy (which had nevertheless given the English deists suggestions and ideas) and in Spain.
Among the various ideas conveyed by the deist current, the fundamental one is that of natural religion, affirmed by d. as the only true and legitimate religion. For this assertion to be soundly founded, it would be necessary to demonstrate either the impossibility of revelation; or its factual nonexistence; or finally that, even if the existence of revelation is admitted, it does not possess such requirements as to demand our assent.
The impossibility of revelation could be maintained only on the presupposition of an impersonal God, who acts not as an intelligent cause and, with regard to operations ad extra, a free one, but as a blind and necessary natural force; that is, on the presupposition of a pantheistically conceived God. The fortunes of this hypothesis are bound up with those of pantheism.
To demonstrate that in fact there has been no revelation, it is necessary to demolish its factual proofs, that is, those deduced from supernatural events. This could be achieved by denying either the very historical reality of such events or their supernatural character. This was the path followed by Reimarus in the work from which Lessing published fragments. On the value of similar attempts, V. especially: JESUS CHRIST; REVELATION.
Setting aside this question, one may instead seek to demonstrate that, even if supernatural facts existed, certainty regarding the propositions of faith could in any case not be deduced from them. The argument here enters the philosophical field; and it was formulated with the greatest technical precision by Lessing: «contingent historical truths can never serve as demonstrations of necessary truths of reason». This principle is closely connected with the general epistemological problem: whether knowledge of the universal and necessary can be attained from the particular and contingent. Kant, as is well known, starts precisely from the negative answer on which empiricists and rationalists agreed, in order to formulate the theory of the synthetic judgment a priori. In the present case, one may in part set this problem aside, provided that the objective validity of the principle of causality is admitted. For what must be proved here from historical facts is not directly the revealed (necessary) truths, but only that God has spoken; hence, from contingent facts, a contingent fact (revelation is, as a fact, contingent, since it is free on God’s part). And the necessary truths of faith derive, properly speaking, not from the contingency of the fact of revelation, but from the necessary truthfulness of the author of this fact.
To reach the ultimate roots of the problem, it would remain only to examine whether from a historical fact one can ascend to God as to a sufficient reason. This problem, however, is merely one aspect of the general question: whether it is possible to ascend from the contingent to God, the necessary Being; on this question V. Dio.
As for its technical meaning in philosophy, d. appears as an inconsequential compromise between agnosticism and theism. It seeks to affirm the knowability of God’s existence while denying the knowability, even analogical, of his nature. But the unknowability of God’s nature also entails that of his existence. For when it is unknown whether God is transcendent or immanent in the world, an intelligent and free cause or a blind natural force, it is in reality unknown whether he exists: for an immanent God (in the pantheistic sense) is God in name only, and a blind force is not God even in name. D. therefore possesses only the apparent consistency of confused concepts.
As soon as it is thought through to the end, that is, genuinely thought, it dissolves: into pure agnosticism, if what d. implies in its negative aspect (the unknowability of the divine nature) is made explicit; into theism or pantheism and atheism, if its positive content (the knowability of God’s existence) is made precise.