We all know “Cogito ergo sum” (or in French, ” Je pense, donc je suis”), “I think, therefore I am”, which comes near the beginning of “Principles”.  This is preceded by an exhortation to a form of radical scepticism casting doubt on every sense, belief and assumption we have about the world.  Only by throwing away everything we took as given, are we able to know what is really true.

However, Descartes regards this as “once in a lifetime” activity for the enquirer, not a position of continuing doubt and uncertainty, but an opportunity through doubt to come to solid bedrock.

He is also very practical, warning:

“… this process of doubt should be restricted to our considering what is true. For as far as the conduct of life is concerned, the moment for action would usually have passed long before we could resolve our doubts. We are often forced to opt for what is only probably right, and sometimes we even have to choose between two equally probable alternatives.” (Part I, Section 7)

In life we often must simply act.

During this once in a lifetime event of radical scepticism, and having come to the position of absolute doubt, the one thing that we can be certain of is the awareness of our own doubt and the surety that there is something/someone, me, who is doubting; hence “cogito ergo sum”.

However, Descartes is then left with the problem of how we can know anything else.  Our senses of the world can be flawed and whilst the fact that we perceive things is further evidence of our own existence (that awareness of perception is part of the ‘cogito’), it gives no reliable evidence of anything else.

Descartes at this point turns to God.  Self examination and a variant of the “ontological argument”² forces him to both believe in an omnipotent and good God, and also that, while our sense are imperfect, God would not give us a fundamentally flawed view of the world.  Our senses are at least partially reliable because of the nature of God; and hence our own personal exploration of the world and the whole scientific endeavour become meaningful.

A constant problem for all non-theistic ethics is how to move from descriptive accounts of particular ethical positions to prescriptive ones of how one should act.  They are morally toothless.  However,  the non-theistic epistemological gap in science is less often discussed.

I recall some years ago, just before I went to university, talking to a mathematics lecturer who was, I believe, an atheist.  He explained to me how he believed the sun would rise every morning, but had no evidence that it would.  Even assuming that our sense are reliable (which Descartes would doubt), we can observe that the laws of physics stay the same and have been the same, but in the end have no reason to believe that this will continue to be the case.  The “law of uniformitarianism” can be observed to have held in the past, but only by reflexively applying the ‘law’ to itself can we assume it will continue to do so.

Science without God is ultimately blind faith.

I was also fascinated by Descartes’ exposition of the nature of emotion and senses (part IV section 190) and surprised at the sophistication of the model of sensory stimulation of nerves (assumed to be mechanical motions), including discussion of phantom limbs, which recur in modern texts.  He talks about our five external senses and two internal ones.  The list of external senses has been fairly stable since Greek times and one of his internal ones would also feature in ‘modern’ lists³, that is the sense we have of stomach, bladder etc., which Descartes relates to our appetites.

The other internal sense is perhaps more interesting, he suggests that motions of the “little nerves” of the heart give rise to emotion.  If the blood stretches in the heart, the expansion is felt as joy; if it is sluggish the lack of expansion of the ventricles is felt as sadness.  Although the exact physical model differs, the general flavour of this is surprisingly modern; current models of complex emotion usually involve some form of interpretation of body, lower brain activity, and hormones and other chemicals in the blood stream and brain.  Descartes describes how calling an event to mind can lead to a bodily reaction which is then felt as the emotion related to the event.  This cycle of thought leading to bodily emotion leading back to feelings is exactly what one would find in a modern account; a holistic view that sees body and mind both distinct in some ways but also intimately connected.

So, if anyone ever describes your work as too Cartesian … be proud.

1. René Descartes, 1644, Principles of Philosophy, trans. George MacDonald Ross, 1998–1999 [back]
2. I have never found the ontological argument for the existence of God particularly convincing, but it continues to cause debate even now nearly 1000 years after Anslem’s first formulation. [back]
3. Now-a-days the list of internal senses would be longer including proprioception (sense of body position) and equilibrioception (sense of balance). [back]