The Substance Dualists also pose that essential qualities of the mind and brain, as made popular by Rene Descartes, disallow for the two to be the same. This, again, relies on the necessity of the conceivability-possibility principle being true. Nevertheless, this argument is still flawed elsewhere. The argument posits that if a body and mind are able to be conceived to withhold their essential qualities while independent from each other, then it must the the case that the two are separate. Immediately one may be able to sniff out the flaw in this argument We could say that when separated, the mind and brain share different essential qualities but that is already to assume that the mind and brain are distinguishable at all. A Physicalist may say that, instead, the mind is simply a different perception of what the brain does. Just as Aristotle first pointed out with the Problem of Explanatory Impotence, that is, if the mind and brain are not necessarily connected then why are they connected at all, we may not presume the qualities of distinct substances until a distinction is proven to exist. Therefore, no distinction is guaranteed and the Substance Dualists are simply playing word