“ The Soul begins to have Ideas when it begins to perceive.
To ask, at what TIME a man has first any ideas, is to ask, when he begins to perceive;—HAVING IDEAS, and PERCEPTION, being the same thing. I know it is an opinion, that the soul always thinks, and that it has the actual perception of ideas in itself constantly, as long as it exists ”
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“and so growing up in a constant attention to outward sensations, seldom make any considerable reflection on what passes within them, till they come to be of riper years; and some scarce ever at all. 9. The Soul begins to have Ideas when it begins to perceive. To ask, at what TIME a man has first any ideas, is to ask, when he begins to perceive;—HAVING IDEAS, and PERCEPTION, being the same thing. I know it is an opinion, that the soul always thinks, and that it has the actual perception of ideas in itself constantly, as long as it exists; and that actual thinking is as inseparable from the soul as actual extension is from the body; which if true, to inquire after the beginning of a man’s ideas is the same as to inquire after the beginning of his soul.” source