There are, however, fundamental difficulties with the argument from analogy. First, if one accepts the Cartesian account of consciousness, one must, in all consistency, accept its implications. One of these implications, as we have seen above, is that there is no logically necessary connection between the concepts of "mind" and "body;" my mind may be lodged in my body now, but this is a matter of sheer contingency. Mind need not become located in body. Its nature will not be affected in any way by the death of this body and there is no reason in principle why it should not have been located in a body radically different from a human one. By exactly the same token, any correlation that exists between bodily behavior and mental states must also be entirely contingent; there can be no conceptual connections between the contents of a mind at a given time and the nature and/or behavior of the body in which it is located at that time.
What makes this odd is that this is not consistent with the Cartesian account of consciousness at all; Descartes explicitly rejects this view. Compare chapter 5 of the Discourse on Method:
And here I specially stayed to show that, were there such machines exactly resembling organs and outward form an ape or any other irrational animal, we could have no means of knowing that they were in any respect of a different nature from these animals; but if there were machines bearing the image of our bodies, and capable of imitating our actions as far as it is morally possible, there would still remain two most certain tests whereby to know that they were not therefore really men. Of these the first is that they could never use words or other signs arranged in such a manner as is competent to us in order to declare our thoughts to others: for we may easily conceive a machine to be so constructed that it emits vocables, and even that it emits some correspondent to the action upon it of external objects which cause a change in its organs; for example, if touched in a particular place it may demand what we wish to say to it; if in another it may cry out that it is hurt, and such like; but not that it should arrange them variously so as appositely to reply to what is said in its presence, as men of the lowest grade of intellect can do. The second test is, that although such machines might execute many things with equal or perhaps greater perfection than any of us, they would, without doubt, fail in certain others from which it could be discovered that they did not act from knowledge, but solely from the disposition of their organs: for while reason is an universal instrument that is alike available on every occasion, these organs, on the contrary, need a particular arrangement for each particular action; whence it must be morally impossible that there should exist in any machine a diversity of organs sufficient to enable it to act in all the occurrences of life, in the way in which our reason enables us to act. Again, by means of these two tests we may likewise know the difference between men and brutes.
Thus from a genuinely Cartesian view the lack of a logically necessary connection between mind and body in general is not relevant to the question. What is relevant is the very different issue of whether there are certain behaviors so constituted that they can reasonably be seen as the effects of a "universal instrument," which (the argument goes) cannot be had in an extended thing. For a Cartesian an unextended universal instrument is a mind; so you can conclude that someone else has a mind by learning what a mind is in one's own case and looking for effects that require it in someone else. The symmetry suggested in the article doesn't exist in the Cartesian view; mind and body have two different ways of operating on their own, and therefore we can tell (at least to some extent) the influence of mind on a body by recognizing cases where bodies act in ways going beyond what a body would do on its own. The Cartesians disagreed about how strong this argument was -- Arnauld, for instance, argued that it could be made demonstrative, and Malebranche argued that it could never be more than a 'conjecture', i.e., a probable argument. But this line of thought was a pretty important part of the Cartesian view of consciousness.
