To remove the doubt that physical things may be known simply through the senses, Descartes examines the piece of wax before and after he heats it by the fire. Before the wax is heated, it still has "the scent of the flowers from which it was collected. Its color, shape, and size are manifest" (Ariew 32). Once it's heated, the wax loses all the properties it had before that Descartes' five senses observed: "the scent is vanishing; the color is changing; the original shape is disappearing" (Ariew 32). Although the wax lost all its qualities that the senses used to identify it as a certain type of physical thing, the wax is still there. Descartes watched the wax as it melted, and witnessed that its properties changed with heat, so he can be sure that this disfigured object is still the same piece of wax as the one before the heating. However if he hadn't observed this change of qualities, Descartes' senses wouldn't have been able to tell him that the honey flavored cold, hard object and the hard liquid with no scent were in fact the same piece of wax. Therefore Descartes reaches the conclusion that the senses are not useful in acquiring knowledge about physical things, it's too likely that they will misguide us with information about qualities that are not essential to substances.
Once he removes the possibility of knowing through senses, Descartes considers the imagination as a source of knowledge. He removes every aspect of the wax acquired through the senses and that doesn't really belong to the wax, and finds himself left only with "something extended, flexible, and mutable" (Ariew 32). He discovers that although he can grasp the ability of the wax to go through innumerable changes regarding its shape, his imagination limits him from grasping what all of these changes actually are. Therefore the imagination is actually as limited as the senses. Although it helps Descartes form some ideas about the changes the wax might go through which his senses would eventually observe, he cannot distinctly picture and learn what all these changes might be through his imagination.
Descartes comes to the realization "that the perception of the wax is neither a seeing, nor a touching, nor an imagining" (Ariew 33). The wax can only be known through an inspection of the mind, which is the only way to achieve a true understanding of what the wax really is. Both the senses and the imagination have their limits; one is unable to grasp the changes a substance can go through, and the other can never clearly and distinctly know what all these changes could be. Descartes believes that the "inspection can be imperfect and confused... or clear and distinct" depending on how closely he pays "attention to the things in which the piece of wax consists" (Ariew 33). He reaches the conclusion that even though his senses help him perceive the physical world around him, he could not reach a conclusion about it if his mind wasn't there to help him make sense of it. He tries to clear this up with the example of looking out of the window to see hats and clothes crossing the street, and understanding that these are some men walking, without actually seeing their faces.
Instead of discussing that a complete understanding free from the limits of the senses and the imagination is only possible by combining the two with the power of the mind, Descartes chooses to disprove that the two can succeed by themselves to create the concept of the inspection of the mind. Although he successfully reaches his conclusion at the end, his technique follows the rigid procedure of all the other Meditations where he keeps removing doubt until the point he wanted to prove is the only option left.
Ariew, Roger, and Eric Watkins, eds. Modern Philosophy : An Anthology of Primary Sources. Boston: Hackett Company, Incorporated, 1998.
