When Pierre was seven years old he was sent to school in Digne, a much larger town across the valley about 10 km from Champtercier. There he learnt Latin and arithmetic and, except for a year spent at school in Riez, he remained in Digne until 1607 :-
At the age of eleven he so impressed the Bishop of Digne with an oration delivered in Latin at the church in Champtercier that the Bishop is said to have declared that "this child will one day be the marvel of his century." On the secular side, during his last two years at school in Digne the young Gassendi composed prosimetric farces in Latin for his fellow schoolboys to perform in the large houses of the town.In 1607, Gassendi left school in Digne and returned to his native village of Champtercier where he spent the next two years. Then in the autumn of 1609 he went to the University of Aix-en-Provence to study philosophy under Père Philibert Fesaye. He clearly was an exceptional student for when Fesaye was absent he asked Gassendi to take the lecture in his place. From 1611, Gassendi studied theology under Professor Raphaelis and, as part of the course, he learnt Greek and Hebrew. While he was studying at Aix, his father Antoine Gassend died (in 1611).
Gassendi was Principal at the College of Digne from April 1612 to 1614. He received a doctorate in theology from the University of Avignon in 1614 and was ordained one year later. He had already been appointed to the minor role of Chanoine of the Cathedral in Digne in 1614. He held this post until 1634 when he was elevated to the higher-ranking position of Prévôt. In April 1615 Gassendi left Provence for the first time, spending the period from April to November in Paris. He had gone there to resolve a dispute concerning his position at Digne, He returned to Aix where he spent the winter of 1615-16, then conducted his first mass in 1616.
In 1617 both the Chair of Philosophy and the Chair of Theology fell vacant at the University of Aix-en-Provence. Gassendi applied for both chairs and was offered both. He chose the Chair of Philosophy, giving the Chair of Theology to his former teacher Père Philibert Fesaye. This appointment as professor of philosophy at the University of Aix was in addition to the positions he held in the cathedral in Digne, which we mentioned above. Gassendi spent six years at Aix where he met Nicolas-Claude Fabri de Peiresc (1580-1637) who became his patron, supporting him financially for many years. Peiresc had attended lectures by Galileo on astronomy and had become so interested that he set up an observatory in 1610. He employed Joseph Gaultier to work for him there and the two were the first people to observe the Orion Nebula in 1610. When Gassendi arrived in Aix he lived at the house of Joseph Gaultier whom he described as having :-
... no difficulty in equalling all the ancient and modern philosophers and mathematicians.Jean-Baptiste Morin also lived in Gaultier's house for he had been employed by Peiresc to assist Gaultier in making observations. Later Morin and Gassendi would become involved in a public dispute but at this stage they were good friends. Gassendi quickly learnt astronomy from Gaultier and so Peiresc also employed Gassendi as part of the team to assist in his project of computing the times of the four moons of Jupiter. We also have records of Gassendi and Gaultier observing a comet in 1618, an eclipse of the moon in 1620, and an eclipse of the sun in 1621.
Gassendi's position at the University of Aix only lasted until 1623 when the Jesuit order took control of the university and he was forced to leave. This was not because the Jesuits had any particular objection to the material that Gassendi was teaching, rather it was just that they dismissed all those who were not Jesuits. He did not hold any further academic posts until 1645 when he was appointed professor of mathematics at the Collège Royale in Paris. However, there is over twenty years of Gassendi's career to look at before we reach that point. His first move on being dismissed from his chair was to travel to Grenoble where he remained until July 1624 after which he resided in Digne. While teaching at Aix he had included his objections to the philosophy of Aristotle in his lectures and he had decided to publish this material. He published Exercitationes I, the first of seven projected volumes of Exercises in the form of paradoxes against the Aristotelians, in Grenoble in 1624. He wrote (see for example ):-
I always made sure that my students could defend Aristotle properly. But at the same time, I also provided as appendices doctrines that would undercut Aristotle's dogmas. Indeed, given the place, the characters and the times, it was necessary to do the former. But not to omit the latter was a matter of candour because those doctrines provided true reason for withholding ascent. ... [I] began to examine the doctrines of other sects to find out whether they might offer something sounder. Although I found perplexities everywhere, none of the doctrines impressed me more than the lauded akatalepsia of the Academics and Pyrrhonians.Gassendi first met Mersenne in October 1623 when he visited Paris. He took with him an introduction from Peiresc and soon Gassendi and Mersenne became good friends. Through Mersenne, Gassendi quickly became acquainted with many leading scholars. From that time on until Mersenne's death in 1648, whenever Gassendi was in Paris he would visit Mersenne and the two would celebrate mass together. Mersenne later tried to persuade him to give up mathematics and theology in favour of philosophy. After returning to Provence from Paris, Gassendi wrote to Galileo with strong support for his argument that the earth revolves round the sun. Gassendi had been intending to produce six further volumes of his Exercitationes but at this time he decided to give up the project. He spent the period between 1625 and 1628 at Grenoble, Aix and Digne. In May 1628 he again travelled to Paris and through his contacts with Peiresc became friendly with François Luillier, the Dupuy brothers, and others from their circle. Pierre and Jacques Dupuy were librarians at the Bibliothèque du Roi, which dated back to the fourteenth century. It had been moved to Paris between 1567 and 1593, and catalogued in 1622. Pierre and Jacques Dupuy travelled throughout France amassing books and manuscripts for the library and, after Gassendi met the brothers, he worked at their library undertaking research on Epicurus.
He spent a few months in the Netherlands, travelling there in December 1628. It was to be his only trip outside France and he travelled widely throughout the country. His work Examination of the philosophy of the doctor Robert Fludd was first published in Holland in 1629. It had been written at Mersenne's request to present the arguments against Fludd's philosophy. In 1632 Gassendi published Mercury seen on the face of the sun, which described his observations of the transit of Mercury which he observed from Paris in November 1631 following the prediction of the event by Kepler in 1629. Gassendi had used a telescope to project the image of the sun onto paper, and so was able to observe the transit. Gassendi continued to publish works on philosophy and astronomy. He believed in atomism and defended a mechanistic explanation of nature, as for example in On the apparent magnitude of the sun on the horizon and overhead (1635). Life became more difficult for Gassendi after his patron Peiresc died in 1637. Although Peiresc left books and mathematical instruments to Gassendi in his will, Peiresc's nephew refused to let Gassendi have them. Gassendi went on to write a biography of Peiresc, published in 1641; it is generally considered the first biography of a scholar. Gassendi later wrote biographies of Copernicus, Puerbach and Regiomontanus.
Mersenne asked Gassendi to review Descartes' Meditations which he did producing Objections in 1641. Descartes did not take kindly to Gassendi's criticisms and replied with a stinging attack in Responses. Gassendi was not going to allow matters to rest there, and replied again, this time with Instantiae which began to circulate in Paris in 1642. Battle lines were drawn, and the two argued their cases in a very public debate. This was not the only public debate that Gassendi was carrying out at this time. The other was with Morin who insisted that the earth was at the centre of the universe. Gassendi was a firm believer in the system of Copernicus and Galileo, and the argument with Morin led to him thinking deeply about the scientific case for a sun centred system. In 1642 Gassendi published On the motion impressed by a moving mover. This book was written to argue against those who claimed that the way heavy bodies fell to the earth proved that the earth could not be moving. He had been saddened by the trial of Galileo in 1633, but had continued to give his full support to Galileo's theories. The year of 1642 when this book was published was actually the year in which Galileo died following nine years of house arrest. Several attacks on this work of Gassendi resulted in his publishing further work supporting the arguments of Galileo entitled On the proportion by which heavy bodies are accelerated.
In 1645, on the recommendation of Cardinal Richelieu, Gassendi was offered the Chair of Mathematics at the Collège Royale in Paris. Although normally an appointment by the king, at this time Louis XIV was only seven years old, and his duties were being carried out by advisors. Gassendi's health was rather poor by this stage in his life, being troubled by a lung complaint. He accepted the Chair of Mathematics on the condition that he would be able to return to Provence when his health was too poor to remain in Paris; he was appointed with this being accepted. He gave his inaugural lecture on 23 November 1645, with Cardinal Richelieu in the audience. He carried out his duties very successfully, lecturing on astronomical topics and carrying out astronomical research. He was assisted by Jean Picard who was an outstanding astronomer. They observed a solar eclipse on 21 August 1645, and lunar eclipses in 1646 and 1647. The results of Gassendi's observations and his lectures were written up and published as Institutio astronomica juxta hypotheseis tam veterum, quam Copernici et Tychonis in 1647. Also in 1647 he published Syntagma Philosophicum which was translated into English and published as Three Discourses of Happiness, Virtue and Liberty in 1699. This English translations begins as follows:-
Mankind having a natural inclination to be happy, the main bent and design of all his actions and endeavours tend chiefly that way. It is therefore an undeniable truth that happiness, or a life free from pain and misery, are such things as influence and direct all our actions and purposes and to the obtaining of them.As he had feared, Gassendi began to find that his health was making it very difficult for him to continue teaching so, as the conditions of his appointment allowed, he left for Provence in 1648. He spent the following years partly in Digne and partly in Toulon; the latter he found particularly good for his health. In 1649 he published Philosophiae Epicuri Syntagma containing his work on Epicurus. Lisa T Sarasohn begins the Preface of  as follows:-
It took the French priest and philosopher Pierre Gassendi more than twenty-five years to complete his project of rehabilitating Epicurus and transforming the philosophy of the ancient atomist into his own system.On 19 September 1648, Florin Périer and some friends performed an experiment suggested by Blaise Pascal on the summit of Puy de Dôme. They found that the height of a mercury column at the summit is 85 mm less than in Clermont-Ferrand 1000 metres below. Despite Gassendi's lung troubles, he was able to climb a mountain on 5 February 1650 with his assistant François Bernier and confirm the findings of the Puy de Dôme experiment. Gassendi remained in Provence until the spring of 1653 when he felt well enough to return to Paris with his assistant François Bernier. He found a circle of mathematical friends, some old some new, including Ismael Boulliau, Blaise Pascal, Gilles de Roberval and Girard Desargues. They met on Saturday mornings, and probably due to their influence, Gassendi produced an anonymous pamphlet attempting to reassure the people of Paris that the predicted eclipse on 12 August 1654 would not lead to a disaster. He was not entirely successful as many of the inhabitants of Paris hid in their cellars on the day the eclipse was predicted. During this period he also published a number of other works, but in November 1654 he became seriously ill. When the better weather came in the following spring he recovered a bit but in August 1655 he became seriously ill again. He was bled by doctors and this, not surprisingly, left him much weaker. He pleaded with doctors not to bleed him again but they continued to administer their 'cure'. He died at the home of Henri-Louis Habert de Montmor, who had been his patron during his final spell in Paris. He was buried in the Montmor chapel at Saint Nicolas-des-Champs. His Complete Works were published in six volumes three years after his death.
Antonia Lolordo writes:-
Gassendi's first biographers more or less agree about his character. They describe him as gentle, easy-going, sociable, candid, and - importantly for someone dependent on patronage and the good will of other intellectuals - humble.
Article by: J J O'Connor and E F Robertson