I'm reading through Locke's An Essay Concerning Human Understanding and it's interesting to read the reasons in which he refutes the notion of innate ideas.
Obviously, it's because he was an empiricist, but more importantly I think it has to do with his notion of powers. Since all ideas (according to Locke) are ideas of either sensation (i.e. external objects cause the perception of an idea) or reflection (i.e. the mind takes its own opetations as objects of understanding), innate ideas (if they exist at all) would be considered ideas of reflection.
Ideas of reflection, like external objects, have a quality (or power) to cause the perception of other ideas. It would make sense to categorize innate ideas as ideas of reflection, however, Locke rejects this for several reasons. He believes that the very first ideas minds perceive are ideas of sensation. That is, ideas of sensation are prior to ideas of ideas of reflection. So, innate ideas, should they be ideas of reflection, cannot be prior to ideas of sensation and therefore cannot be considered innate.
Let's suppose that innate ideas are lodged in the faculty of retention (of which memory is a part) since innate ideas are imprinted on the human mind upon birth. Well if that were the case, people would readily revive past perceptions of ideas from memory. If innate ideas are within memory, a child would be able to recount those innate ideas, however, that's not the case (try asking for example, it's possible for the same thing to be and not to be or other supposed innate ideas like God, etc.). That is why innate ideas, should they exist at all, have no qualities by which they can be perceived by the mind.
I think I might just be reciting Locke's entire refutation of innate ideas, but I think it's interesting to ask if a thing can exist without qualities (more specifically, if an idea can exist within the mind without being able to be perceieved). I suspect this has to do with realism and nominalism. What do you guys think?