In deriving our knowledge from two distinct sources, Sensation and Reflection, Locke is advancing a position altogether different from that of what is properly called the Sensationalist school of philosophers. Gassendi and Hobbes before him, Condillac and Helvétius after him, found the ultimate source of all our knowledge in the impressions of sense. The emphatic words of Hobbes, standing in the forefront of the _Leviathan_, are:--"The original of all the thoughts of men is that which we call Sense, for there is no conception in a man's mind which hath not at first, totally or by parts, been begotten upon the organs of sense." And Condillac, aiming at a theory still more simple, derives from sensations not only all our knowledge but all our faculties. "The other fountain," then, of Locke has, we must recollect, a peculiar significance as distinguishing his psychology from that of the sensationalist writers who preceded and who followed him. His theory of the origin of knowledge may fairly be called an experiential, but it cannot with any truth be called a sensationalist theory. The rest of the Second Book of the _Essay_ is mainly taken up with the attempt to enumerate our simple ideas of Sensation and Reflection, and to resolve into them our other ideas, however complex. To follow Locke into these details would be to re-write the _Essay_. I propose simply to direct the attention of the reader to a few salient points. Of "Simple Ideas of Sensation," some "come into our minds by one Sense only." Such are the various colours, sounds, tastes, and smells, Heat and Cold, and the sensation of Resistance or Impenetrability, which Locke denominates Solidity. "The Ideas we get by more than one sense are of Space or Extension, Figure, Rest, and Motion." The "Simple Ideas of Reflection," which the mind acquires, when "it turns its view inward upon itself, and observes its own actions about those ideas it has received from without," are mainly two, namely, Perception or Thinking, and Volition or Willing. "There be other simple ideas, which convey themselves into the mind by all the ways of Sensation and Reflection, namely, Pleasure or Delight, Pain or Uneasiness, Power, Existence, Unity. (Bk. II., ch. vii., § 1.)