idiot

A person who is unintelligent as opposed to simply refusing to think.

This is where the saying "you cant fix stupid" comes into play, an idiot can be taught but a stupid person doesn't want to use what you teach them.

Another definition is Patrick (star).
An example is someone who was never told how to read, they are not incapable just ignorant and waiting to learn.

That person is one of the biggest idiots I have ever meet, he didn't know what spray paint was.