We may not be able to account for consciousness, yet the fact that we are conscious is one thing of which we are absolutely certain. This realization was one of René Descartes’s great contributions to Western philosophy, some three hundred and fifty years ago. Like many philosophers before and since, Descartes was looking for absolute truth. To this end, he created his method of doubt. Anything that was open to doubt, he argued, could not be the absolute truth.