Cartesianism that swept through Christian Europe during the enlightenment had a profound effect on how minds, bodies and other animals are understood. Although no one (almost no one just to be safe) these days ascribes to Descartes mind-body dualism, the influence remains. As Lyon and Keijzer (2007) have pointed out, the Cartesian framework has been a huge influence in species-centrism by dividing the world into two stuffs, one exclusive to humans.
Descartes view of the workings of nature, which was partly due to reaction to the Aristotelian view, had profound effects on how minds and bodies are understood. The Aristotelian framework, as outlined by Matthews (1977) placed humans in a continuum with animals and plants. What distinguishes humans from other animals is the possession of a rational soul - our capacity for volition, intellection and rationality.However, when it comes to sensory experience – sensing, perceiving, imagining, and having emotions, we are practically on the same page as animals. Rationality, it seems, is what marks us different from animals. According to the Aristotelian view, there is a necessary connection between mentality (consciousness) and life and a separation of life and mechanisms. According to the Aristotelian view, the soul is ordered hierarchically. At the lowest level are plants with vegetative souls. Animals on the other hand differ from plants as they were seen as capable of sense perceptions, emotions, locomotion and so on, and supposedly possess sensitive souls.
Descartes breaks with the traditional Aristotelian view by rejecting both the connection between life and consciousness and the separation of life and mechanisms. While the Aristotelian view placed a division between the living and the non-living, Descartes postulates a continuum where living and non-living things operate in a similar way. All living things are mechanics of some sort in which the workings can be explained on the basis of mechanical principles. Descartes had a clear distinction between mind and body as two separate substances. Bodies according to Descartes are mere machines that can be explained in mechanical principles while the mind/thought, mentality in general, cannot be explained in mechanical principles and are not a property of any kind of body, natural or artificial. All non-human animals are without minds. They are simply complex machines whose behaviour can be explained without reference to mental phenomena. Descartes saw no connection between mind/thought and life since it’s not bodies that think in the first place.
One cannot entail ‘x is alive’ from ‘x is conscious’ because for Descartes it is possible to be conscious without having a body. A body is required for something to be alive and that it must be possible for the mind to exist without being alive. As Matthews puts it ‘kind of entity, mind, which is self-transparent; for any act it performs and any state it is in, it cannot doubt that it performs that act or is in that state’.
Descartes did not deny that the body and mind causally interact ‘intermingle’, with each other. The location of contact between mind and body was supposedly the pineal gland in the brain. For Descartes mentality is not restricted to rationality, rather it is simply anything which we are aware and conscious of, such as our sensory experience and intellection. The essence of the mind then is to be conscious of its acts, be it intellection or volition, without which it would not exist.
Descartes’s dilemma arises in attempting to classify sensory experience as either part of the mind or the body but not both. If sensations are part of the mind then animals do not have any since, according to Descarte, animals lack minds. On the other hand if sensations are part of the body, it would be contradictory to have them at the same time as being deceived into having a body when we do not (as per his argument that we could be deceived by an evil demon into thinking that we are experiencing the heat of fire).
Sensation as a mode of thought means sensation occurs in the mind. We can then infer that animals have sensations, as they feel pain for example. This however contradicts Descartes argument that animals have no minds. If sensation is taken as a mode of thought then Descartes has to accept that animals have minds (as they experience sensations). The other alternative is to regard sensation as a mode of extension, which is a bodily process. The problem with this alternative is that assuming that an evil demon could deceive me into thinking that I am sitting before the fire, feeling its heat and seeing its flames, even though I had no body, seems inconsistent as it would not be possible to experience the fire without a body since the sensation involved in these experiences are bodily occurrences and I had no body. Descartes is forced to say that, although sensory experience is not essential to minds, it is a property of the mind as it only occurs in minds. Descartes had to deny that non-human animals have sensory experience as he had denied them minds.
This view is not acceptable anymore nor is defended (as far as I know) by any contemporary thinker. However, the reminiscence remains and is evident in the way we go on about thinking and understanding the human condition. This is pointed out by Lyon and Keijzer’s discussion of the anthropogenic approach to cognitive explanation which was championed by Descartes. Often the human mind is assumed as a starting point (and the focus), analytical introspection is used as a method, and the often unstated distinction between human beings and the rest of the natural world still lurk within most cognitive science theorising and researches.