Locke's Essay on the Human Understanding was an event that made an epoch in philosophy, because its author, not satisfied to take up questions where his predecessors had left them, undertook an independent examination of the Human Mind, in order to ascertain what were the conditions of its knowledge. The ability with which this attempt was made, the entire sincerity of it, the patient watch of the mental operations, the sagacity that followed the trail of lurking thoughts, surprised them in their retreats, and extracted from them the secret of their combinations, fairly earned for him the title of "Father of Modern Psychology." The intellectual history of the race shows very few such examples of single-minded fidelity combined with rugged vigor and unaffected simplicity. With what honest directness he announced his purpose! His book grew out of a warm discussion among friends, the fruitlessness whereof convinced him that both sides had taken a wrong course; that before men set themselves upon inquiries into the deep matters of philosophy "it was necessary to examine our own abilities, and see what objects our understandings were or were not fitted to deal with." To do this was his purpose. "First," he said, "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. "Secondly, I shall endeavor to show what knowledge the understanding hath by those ideas, and the certainty, evidence and extent of it. "Thirdly, I shall make some inquiry into the nature and grounds of faith or opinion; whereby I mean that assent which we give to any proposition as true, of whose truth we have yet no certain knowledge; and we shall have occasion to examine the reasons and degrees of assent."