  Leibniz, the other important Rationalist defender of innateness, elaborates the theory in a number of important ways in his New Essays on Human Understanding. He famously challenges Locke’s analogy of the mind as blank slate with a competing image of the mind as a block of marble whose veins already mark out the shape of Hercules (52). A more significant point is his sharpening of the poverty of the stimulus claim. He argues that our experience of the world is always of contingent particulars, but our knowledge can be general, and sometimes necessary (50). Going back to the Meno example, the slave can see that the squares Socrates has scratched out in the dirt stand in a certain relation, but he ends up knowing that such a connection must hold of any possible set of squares that meets Socrates’ initial description; that it holds – to use a phrase Leibniz introduced – in all possible worlds. Leibniz argues that rationality must involve more than induction from contingent experience. It must ultimately rely on innate ideas and principles that allow us to grasp not just how things happen to be, but also why they must be that way.