John Locke (1632–1704), one of the Enlightenment's most representative thinkers, born into a culture increasingly defined by a belief in the verity of empirical science and its procedures, solves the problem of metaphor by rejecting both of its aspects. In An Essay Concerning Human Understanding (1690), Locke holds that the foundations of thought are simple ideas, which are obtained through direct sense impressions. From this perspective, words should refer to things and the most that may be expected of language is that it further discursive "Order and Clearness." As for metaphor and "all the [other] artificial and figurative application of Words Eloquence hath invented, [these] are for nothing else but to insinuate wrong Ideas, move the Passions, and thereby mislead the Judgment" (Locke, p. 508). In order to get at the "true ideas upon which the inference depends," Locke advises that from language one should "strip" the "superfluous ideas" evoked by tropes and figures, and then "lay the naked Ideas on which the force of the argumentation depends, in their due order." Thus confronted with "true ideas" in their natural order, the mind easily perceives the truth of things and their relations (Locke, p. 676).
To Locke, metaphor's enigmatic power to create images and ideas is so corrupting of thought that he entirely exiles it from his model of consciousness and (correct) philosophical process. Of course, neoclassical thinkers, such as Voltaire (1694–1778) and Samuel Johnson (1709–1784), continued to use and productively discuss figured language—but in a context whose emphases denied relativism and forestalled the exploration of categories such as the primitive and the irrational.
Giambattista Vico's (1668–1744) views are a notable exception to the late-Enlightenment outlook and its limited and generally dismissive idea of metaphor. Although not influential in his lifetime, Vico's ideas clearly anticipate aspects of the Romantics' intense interest in and philosophical linking of poetic language, primitivism, and psychological and historical relativism. Vico's thought thus demonstrates both the continuities and differences between Enlightenment and Romantic thinking about metaphor.