For in bare naked perception, the mind is, for the most part, only passive; and what it perceives, it cannot avoid perceiving.
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“Though thinking, in the propriety of the English tongue, signifies that sort of operation in the mind about its ideas, wherein the mind is active; where it, with some degree of voluntary attention, considers anything. For in bare naked perception, the mind is, for the most part, only passive; and what it perceives, it cannot avoid perceiving. 2. Reflection alone can give us the idea of what perception is.
What perception is, every one will know better by reflecting on what he does himself, when he sees, hears, feels, &c., or thinks, than by any discourse of mine.” source