Rene Descartes (March 31, 1596 – February 11, 1650) was a highly influential mathematician, scientist and philosopher. Descartes is widely considered to be the 'Father of modern Philosophy'. His most influential work is Meditations on First Philosophy ('First Philosophy being metaphysics). Descartes advocates a method of radical doubt, now labeled Cartesian doubt, whereby the reader, or meditator, begins to doubt all external objects of sense perception and focus only on what the mind 'clearly and distinctly' perceives to be true. Descartes discovers the now well known proposition 'I think, therefore, I am' (known as cogito ergo sum). Descartes unique idea was to start from axiomatic principles that could not be doubted, and proceed to discover truths and certainty from these axioms. He argued that the mind and rational thought, not experience, is the source of all knowledge. This is why Descartes is know seen as a 'Rationalist'. His method is opposed to a more Newtonian or Aristotelean principle of deriving the axioms from the objects of sense experience.