Indeed, the theism of Locke's Essay on the Human Understanding undermined even his Unitarian Scripturalism, inasmuch as it denies, albeit confusedly, that revelation can ever override reason. In one passage he declares that "reason is natural revelation," while "revelation is natural reason enlarged by a new set of discoveries communicated by God immediately, which reason vouchsafes the truth of." [475] This compromise appears to be borrowed from Spinoza, who had put it with similar vagueness in his great Tractatus, [476] of which pre-eminent work Locke cannot have been ignorant, though he protested himself little read in the works of Hobbes and Spinoza, "those justly decried names." [477] The Tractatus being translated into English in the same year with the publication of the Essay, its influence would concur with Locke's in a widened circle of readers; and the substantially naturalistic doctrine of both books inevitably promoted the deistic movement. We have Locke's own avowal that he had many doubts as to the Biblical narratives; [478] and he never attempts to remove the doubts of others. Since, however, his doctrine provided a sphere for revelation on the territory of ignorance, giving it prerogative where its assertions were outside knowledge, it counted substantially for Unitarianism insofar as it did not lead to deism.
See the Essay, bk. iv, ch. xviii. Locke's treatment of revelation may be said to be the last and most attenuated form of the doctrine of "two-fold truth." On his principle, any proposition in a professed revelation that was not provable or disprovable by reason and knowledge must pass as true. His final position, that "whatever is divine revelation ought to overrule all our opinions" (bk. iv, ch. xviii, § 10), is tolerably elastic, inasmuch as he really reserves the question of the actuality of revelation. Thus he evades the central issue. Naturally he was by critical foreigners classed as a deist. Cp. Gostwick, German Culture and Christianity, 1882, p. 36. The German historian Tennemann sums up that Clarke wrote his apologetic works because "the consequences of the empiricism of Locke had become so decidedly favourable to the cause of atheism, skepticism, materialism, and irreligion" (Manual of the Hist. of Philos. Eng. tr. Bohn ed. § 349).