ABSTRACT
One approach to the search for an answer to a fundamental question is to seek a certain or indubitable starting-point. Any such starting-point must be certain, not in the sense of a merely psychological certainty, in which we feel certain, but in the sense of a justified, rational certainty. Here we can recall how Descartes proposed a way of systematic doubt so that he could end up with just this. He claimed to have found it in his famous cogito ergo sum, that is, ‘I think, therefore I am.’ But unfortunately, as many have seen, Descartes’ starting-point is fatally flawed. It is true that we can doubt the evidence of our senses. It is also true that we can, at a pinch, doubt our most primitive mathematical intuitions, for if we find that we are sometimes mistaken when we multiply, say, eleven and twelve, how can we be absolutely certain that we are not having a mental aberration when we multiply two and two, or that our memory about the meaning of mathematical terms is not playing us tricks? But when Descartes insists that even when we doubt these things it is certain that there is an ‘I’ that doubts, he assumes that the ‘I’ is, as he calls it, a thinking thing – that is, an entity that endures, unchanged, through time. But this can certainly be doubted, and indeed is rejected by many thinkers.
