There is an old joke that goes: Rene Descartes went into his local for a drink. When he had finished his first drink the bartender said, “Mr Descartes would you like another?” To which Rene replied “I don’t think…” and disappeared!
To understand the joke you need to know that Rene Descartes, the 17th century French philosopher and mathematician, often regarded as the father of modern philosophy, coined the phrase ‘I think, therefore I am’ (Cogito ergo sum). You are probably familiar with Descartes’ other great contribution in the field of geometry, even if you are unaware, because every time you see a graph with an x-y axis you are seeing Descartes work, as he invented the Cartesian representation that you see.