The Eighteenth Century Enlightenment figures (Diderot, Voltaire, Bayle, etc) believed Locke to have been the chief spokesperson for the theory of knowledge named Empiricism. But not everything he wrote seems quite consistent with Empiricism's central thesis.
A) State that central thesis of Empiricism as you find it in Locke's Essay on Human Understanding.
B) Point to the glaring inconsistency with his own thesis you notice Locke committing.