The concept of Mind-Body dualism is one that has its roots in early classical philosophy, with both Plato and Aristotle setting out strong arguments for this philosophy of the mind. The most famous proponent of this theory though is the “father of Modern Philosophy”, René Descartes. This belief fundamentally stems from the appearance of humans having both mental and physical properties, properties which seem to be radically different. As a response to this Descartes proposed that these properties are contained within two radically different substances, res cogitans, or thinking substance, and res extensa, extended substance. This thinking substance is what makes up a mind and the extended substance a body. Within his Discourse on Method and the Meditations, Descartes outlines three arguments for this distinction between the mind and the body. These arguments, varying in their strength, have been analysed fervently since Descartes published them, and much philosophy of the mind centred on Descartes theses until the beginning of the last century and debate still remains today. The first argument that Descartes sets out in his Meditations for mind body distinctness is what has become known as the doubting argument. This argument first appeared in the Discourse (Descartes, 1971, pp. 32) and he expanded upon it in the Meditations (Descartes, 1641, 2:6). Though the argument changed structure slightly between the two texts it can be broadly seen as: P1- I can doubt that my body exists
P2- I cannot doubt that my mind exists
P3- Identical substances must have identical properties
C- My mind and body are different substances.
It should be noted before examining this argument further that the third premise is a general principle of Descartes’s employed in much philosophical discussion. This principle states that if something is true of X and not true of Y then they are distinct, or in other words if X has some property that Y does not they are entirely different things. This principle is commonly referred to as Leibniz’s Law, or the Principle of the Indiscernibility of Identitcals. Descartes has previously shown in his meditations that all corporeal, physical things can be doubted and should not be assumed to exist. This is shown using his dream, deceiving god, and the evil demon arguments. Premise one then directly follows form the conclusions of this section in the meditations. He also previously concluded that the existence of the mind is indubitable, with his famous conclusion cogito ergo sum, or I think therefore I am (Descartes, 1641, 7:140). Descartes’ second premise in this argument follows wholly from this assertion and cannot be questioned. The third premise, sometimes missing in analyses of the argument, is simply the principle of the indiscernibility of Identitcals. Though this premise is needed for the argument to flow logically its inclusion causes Descartes much difficulty. The strongest criticism of this argument is that this doubt is not a property of the substance; rather it is a property of the observer. In other words, doubt about the existence of the thing does not come from what the substance is, but rather from ignorance on the part of Descartes. Many examples have been used to highlight the inherent weakness in this argument. Perhaps the earliest of these objections came from Antoine Arnauld in 1641 within his Fourth Objections. (http://www.earlymoderntexts.com/pdf/descobje.pdf, pp. 56-57) Here Arnauld uses the example of a right angled tri angle to show the flaw in Descartes reasoning. He says that while a person may not doubt that an triangle is right angled, he can at the same time doubt that Pythagoras’s theorem holds. The person observing the triangle obviously does not have a clear and distinct perception of the triangle but how, Arnauld asks, is “But how is my perception of the nature of my mind any...