Analysis of the Phenomena of the Human Mind Volume I

From the INTRODUCTION:

"I shall inquire into the original of those ideas, notions, or whatever else you please to call them, which a man observes and is conscious to himself he has in his mind; and the ways whereby the understanding comes to be furnished with them."
—Locke, i. 1, 3.

PHILOSOPHICAL inquiries into the human mind have for their main, and ultimate object, the exposition of its more complex phenomena.

It is necessary, however, that the simple should be premised; because they are the elements of which the complex are formed; and because a distinct knowledge of the elements is indispensable to an accurate conception of that which is compounded of them.

The feelings which we have through the external senses are the most simple, at least the most familiar, of the mental phenomena. Hence the propriety of commencing with this class of our feelings.