A friend of the La Mettrie family, François-Joseph Hunauld, who was about to take the chair of anatomy at the Jardin du Roi, seems to have influenced him in this decision.

In 1742 La Mettrie left his family and travelled to Paris, where he obtained the appointment of surgeon to the Gardes Françaises regiment, taking part in several battles during the War of the Austrian Succession.

[3] It was in these years, during an attack of fever, that he made observations on himself with reference to the action of quickened blood circulation upon thought, which led him to the conclusion that mental processes were to be accounted for as the effects of organic changes in the brain and nervous system.

So great was the outcry caused by its publication that La Mettrie was forced to quit his position with the French Guards, taking refuge in Leiden.

[5] There he developed his doctrines still more boldly and completely in L'Homme machine, a hastily written treatise based upon consistently materialistic and quasi-atheistic principles.

[3] La Mettrie's materialism was in many ways the product of his medical concerns, drawing on the work of 17th-century predecessors such as the Epicurean physician Guillaume Lamy.

[6] The ethical implications of these principles would later be worked out in his Discours sur le bonheur; La Mettrie considered it his magnum opus.

[7] Here he developed his theory of remorse, i.e. his view about the inauspicious effects of the feelings of guilt acquired at early age during the process of enculturation.

This was the idea which brought him the enmity of virtually all thinkers of the French Enlightenment, and a damnatio memoriae[8] which was lifted only a century later by Friedrich Albert Lange in his Geschichte des Materialismus.

La Mettrie believed that man worked like a machine due to mental thoughts depending on bodily actions.

He argued that events such as a beheaded chicken running around, or a recently removed heart of an animal still working, proved the connection between the brain and the body.

La Mettrie's extreme beliefs were rejected strongly, but his work did help influence psychology, specifically behaviorism.

[13] Nonetheless, the backlash he received was so strong that many behaviorists knew very little to nothing about La Mettrie and rather built off other materialists with similar arguments.

So strong was the feeling against him that in 1748 he was compelled to leave for Berlin, where, thanks in part to the offices of Maupertuis, the Prussian king Frederick the Great not only allowed him to practice as a physician, but appointed him court reader.

[5] There La Mettrie wrote the Discours sur le bonheur (1748), which appalled leading Enlightenment thinkers such as Voltaire, Diderot and D'Holbach due to its explicitly hedonistic sensualist principles which prioritised the unbridled pursuit of pleasure above all other things.

The French ambassador to Prussia, the comte de Tyrconnel, grateful to La Mettrie for curing him of an illness, held a feast in his honour.

It was claimed that La Mettrie wanted to show either his power of gluttony or his strong constitution by devouring a large quantity of pâté de faisan aux truffes.

[3][9] Frederick the Great gave the funeral oration, which remains the major biographical source on La Mettrie's life.

La Mettrie's collected Œuvres philosophiques appeared after his death in several editions, published in London, Berlin and Amsterdam.