Descartes' Thoughts On Bodies

Descartes points out that the external senses passively perceive the qualities of bodies, such as their "figure, hardness, roughness, ECT." We have simple ideas of bodies, such as "figure, extension, motion, ECT," and complex ideas which are "in some way compounded out of these."

"By the body I understand all that which can be defined by a certain figure: something which can be confined in a certain place, and which can fill a given space in such a way that every other body will be excluded from it; which can be perceived either by touch, or by sight, or by hearing, or by taste, or by smell: which can be moved in many ways." He uses an example of a piece of wax to illustrate this. Think of a piece of wax, think of its sense qualities, color, odor, figure, size, texture, coldness, and the noise when you thump it. Now, suppose we place it close to a fire, and the piece of wax melts. All that you know of the wax has now changed because it melted. Yet, it is the same wax, despite all these changes. Hence the sense qualities cannot constitute the essence of the wax.