Descartes famously began by enquiring whether there is any knowledge so certain that no reasonable person can doubt it. And his celebrated answer to this central question was to say that at least he could not doubt that he doubted; and if he doubts then he must think; and if he thinks he must exist. Cogito, ergo sum. What could be more reasonable than that?
What could be sillier? Descartes' conclusion is absurd, though it took Wittgenstein to demonstrate this. When Descartes says, "I think therefore I am", he must be using a language. But a private language - one that is spoken and understood by only one person - is a contradiction in terms. The concept of meaning is a public concept. And language is a public phenomenon.
But the Cogito was only the bottom of the garden path so to speak. The tradition of subjectivism and transcendental egotism based on Descartes' philosophy has been perpetuated over four centuries, corrupting not only our epistemology but our moral thought and social understanding. Descartes' "cogito" had a thoroughly technical meaning that was neither "thinking" nor "feeling"; a better translation might be, "Something is doubting that anything exists. Therefore something exists." But this would not fit so well on a T-shirt; and as his influence grew, "cogito" changed to mean something like: "I feel, therefore I am real."
In this form, Cartesian subjectivism was consolidated by Rousseau and the Romantic Movements. Its religious expression was found in such as Wesley whose criterion for redemption was to have one's individual heart "strangely warmed" - an ominous pre-echo of the nauseating consumerist revivalism of our own times which advertises Jesus Christ as my personal saviour, as if the dynamics of the forgiveness of sins were the business of insurance companies.
The "I" in "I think therefore I am" is a tyrant. This romantic individual is not only the demonic artist of 19th-century concert platforms and countless embarrassing Hollywood movies about artistic geniuses: he is also the supposedly omniscient personality inside each one of us.
Descartes' faulty epistemology lies behind the moral relativism which plagues modern societies and renders impotent all efforts at ethical consensus. It is not even as though Descartes had delivered to us an unpalatable truth - that the individual personality is sovereign and we must somehow learn as a society to cope with this fact. For the individual constructed on Descartes' model and subsequently elaborated to ever more sickening effect is, as Wittgenstein pointed out, a logical and a grammatical fiction.
There is another slogan, one that may be trusted: you are what you eat. But we have failed to understand that this truth applies not only to the body but to the mind and morals. The subjectivist view that everyone's opinion is equally valid leads to the relativism which claims that the Sex Pistols are as good as Bach. This is a judgement which could only be made by one who had imbibed the culture of the Sex Pistols but not the culture of Bach.
Once the individual has been accepted as an indivisible, unchallengable whole, set apart from everything else in the world, we lose the ability to judge between individual preferences. We must rediscover the pre-Cartesian knowledge that tradition preserves objective beliefs which are more certain than our poor subjectivities. It is futile to say that everyone has a right to their own opinions, as if this means that all opinions, however unschooled and ill-considered, are equally likely to express the truth.
We are what we eat. We form our judgements out of the stuff of which we are constituted. If therefore a child is filled up with the moral and aesthetic equivalent of junk food then we must expect him to develop a junk mind. The most appropriate way to celebrate the 400th anniversary of Descartes is to begin again his quest for understanding but to begin with the realisation that our identity is not something to be deduced absurdly from our own thoughts. The "I" is not something conjectured into existence: it is given and created out of whole worlds of objective values. And it is the choice of values which is crucial. As Ezra Pound said, "Show me what you value and I'll tell you what you're worth."