Comparison Of Descartes And Heidegger According to Descartes, the essence of material substance is simply extension, the property of filling up space. (Med. V) So solid geometry, which describes the possibility of dividing an otherwise uniform space into distinct parts, is a complete guide to the essence of body. It follows that there can be in reality only one extended substance, comprising all matter in a single spatial whole. From this, Descartes concluded that individual bodies are merely modes of the one extended being, that there can be no space void of extension, and that all motion must proceed by circular vortex.
Thus, again, the true nature of bodies is understood by pure thought, without any information from the senses. 1. The Dream Problem Second, Descartes raised a more systematic method for doubting the legitimacy of all sensory perception. Since my most vivid dreams are internally indistinguishible from waking experience, he argued, it is possible that everything I now perceive to be part of the physical world outside me is in fact nothing more than a fanciful fabrication of my own imagination. On this supposition, it is possible to doubt that any physical thing really exists, that there is an external world at all. (Med.
I) Severe as it is, this level of doubt is not utterly comprehensive, since the truths of mathematics and the content of simple natures remain unaffected. Even if there is no material world (and thus, even in my dreams) two plus three makes five and red looks red to me. In order to doubt the veracity of such fundamental beliefs, I must extend the method of doubting even more hyperbolically. In the Sixth Meditation, Descartes finally tried to eliminate the dream problem by proving that there is a material world and that bodies do really exist. His argument derives from the supposition that divinely-bestowed human faculties of cognition must always be regarded as adequately designed for some specific purpose. Since three of our faculties involve representation of physical things, the argument proceeds in three distinct stages.
(Med. VI) First, since the understanding conceives of extended things through its comprehension of geometrical form, it must at least be possible for things of this sort to exist. Second, since the imagination is directed exclusively toward the ideas of bodies and of the ways in which they might be purposefully altered, it is probable that there really are such things. Finally, since the faculty of sense perception is an entirely passive ability to receive ideas of physical objects produced in me by some external source outside my control, it is certain that such objects must truly exist. The only alternative explanation for perception, Descartes noted, is that god directly puts the ideas of bodies into my mind without there acutally being anything real that corresponds to them. (This is precisely the possibility that Malebranche would later accept as the correct account of the material world.) But Descartes supposed that a non-deceiving god would never maliciously give me so complete a set of ideas without also causing their natural objects to exist in fact.
Hence, the bodies I perceive do really exist. Among the physical objects I perceive are the organic bodies of animals, other human beings, and myself. So it is finally appropriate to consider human nature as a whole: how am I, considered as a thinking thing, concerned with the organism I see in the mirror? What is the true relation between the mind and the body of any human being? According to Descartes, the two are utterly distinct. The Sixth Meditation contains two arguments in defence of Cartesian dualism: First, since the mind and the body can each be conceived clearly and distinctly apart from each other, it follows that god could cause either to exist independently of the other, and this satisfies the traditional criteria for a metaphysical real distinction. (Med.
VI) Second, the essence of body as a geometrically defined region of space includes the possibility of its infinite divisibility, but the mind, despite the variety of its many faculties and operations, must be conceived as a single, unitary, indivisible being; since incompatible properties cannot inhere in any one substance, the mind and body are perfectly distinct. (Med. VI) This radical separation of mind and body makes it difficult to account for the apparent interaction of the two in my own case. In ordinary experience, it surely seems that the volitions of my mind can cause physical movements in my body and that the physical states of my body can produce effects on my mental operations. But on Descartes's view, there can be no substantial connection between the two, nor did he believe it appropriate to think of the mind as residing in the body as a pilot resides within a ship.
Although he offered several tenatative suggestions in his correspondence with Princess Elizabeth, Descartes largely left for future generations the task of developing some reasonable account of volition and sensation, either by securing the possibility of mind-body interaction or by proposing some alternative explanation of the appearances. Philosophy Essays.