  Cockburn’s earliest philosophical work, the Defence is a response to the work one of Locke’s critics, Thomas Burnet. In a series of critical pamphlets, Burnet raised doubts concerning the tenability of Locke’s epistemology as a foundation for, among other things, moral knowledge. In the Essay and other works, Locke had suggested that morality could be known by reason and had emphasized the demonstrative character of morality – thereby making a claim to the certainty with which moral ideas could be known. However, Locke never provided an explicit account of how fundamental moral ideas are derived. Burnet concludes that Locke’s epistemology is simply insufficient to the task, and that moral ideas, on Locke’s system, remain as uncertain as the ideas of God’s nature and the immortality of the soul. Burnet uses his critique of Locke as the springboard for his own moral position, one best described as a brand of moral sense theory, in which conscience is the human capacity for empirically discerning the moral value of acts. In other words, for Burnet, one can, upon observing a given set of circumstances, know with immediate certainty whether that act is morally good or evil.