## Pascal, Blaise ( 1623 - 1662 )

**F**rench philosopher, physicist and mathematician, born in Clermont-Ferrand in 1623 and died in Paris in 1662.

**A**fter his mother died when he was three years old, his father moved his family to Paris in 1630. He was a young genius whom his father soon initiated into geometry and introduced into Mersenne’s circle, Académie Parisiensis, of which he was also a member. He familiarized himself with Girard Desargues’ ideas and, in 1640, wrote his essay on conics (Essai pour les coniques), which contained what is now known as Pascal’s theorem.**T**he appointment of his father as royal tax commissioner forced them to move to Rouen, where Pascal developed a new interest in the design and construction of a calculating machine. Some examples of the model that he devised still survive. Some of its underlying principles were later used in modern mechanical calculators.**I**n Rouen, he began to take an interest in physics, and especially hydrostatics, and began his first vacuum experiments. He was involved in the controversy surrounding the existence of horror vacui in nature and he ran important experiments (especially the Puy de Dome experiment in 1647) in support of Torricelli’s explanation of how the barometer worked.**I**llness caused him to return to Paris in the summer of 1647. The doctors advised him to take a break. This marked the beginning of a mundane period ending with his mystical experience of the 23 November 1654. This experience led to his second conversion (in 1645 he had embraced Jansenism), where he became convinced that Christianity and not in philosophy paved the way to God. As a result he put a stop to almost all his scientific work.**A**few months earlier, as reported in his correspondence with Fermat, he had been working on the properties of the arithmetic triangle now known as Pascal’s triangle. This triangle determines the coefficients that arise in successive binomial expansions. His treatment of the triangle in terms of a “geometry of chance” made him one of the founders of the mathematical calculation of probabilities**I**n 1658, apparently to get over a toothache, he developed his study of the cycloid. This turned out to be a major stimulus for the development of differential calculus. As of 1655, he frequented Port-Royal, to where his sister Jacqueline had retired in 1652. He took sides in favour of Arnauld, the general of the Jansenists, and anonymously published his Provincial Letters. The success of the letters led him to plan a defence of the Christian religion.**H**is worsening health as of 1658 frustrated the project, but scattered notes were later compiled in his famous Thoughts (Pensées sur la religion, 1669). Although he always rejected the possibility of establishing rational proof of the existence of God, whose infinity he considered beyond reason, he did admit that the latter could pave the way for faith to combat scepticism. Pascal’s famous wager analyses belief in God in terms of a wager on His existence, for nothing is really lost if man believes and it turns out that God does not exist. The tension between science and religion in his thought was reflected in his admission of two principles of knowledge: reason (esprit géométrique), which is oriented to scientific truths and proceeds systematically from definitions and assumptions through demonstration to new propositions, and heart (esprit de finesse), which does not use systematic procedures because it has a power of immediate, sudden and total understanding in intuitive terms. The heart harbours the source of discernment necessary for selecting the values on which reason should found its work.