In very different fashion does the book set to work that already in its very title declares that man is a machine. While the 'Natural History of the Soul' was cautious, cunningly arranged, and only gradually surprising us with its results, here, on the contrary,the final conclusion is expressed at the outset of the work. While the 'Natural History of the Soul' allied itself with the whole Aristotelian metaphysics only in order to prove by degrees that the soul is but an empty form, into which we may pour a materialistic content, here we no longer deal in all those fine distinctions.

The last chapter... bears the title, " Narratives which prove that all Ideas are derived from the Senses." ...Everywhere the consequence is drawn that only the education he receives through the senses makes man man, and gives him what we call the soul, while no development of the mind from within outwards ever takes place.

The very much shorter section on the rational soul discusses freedom, reflection, judgment, and so on, with the same strong leaning to Materialism there follows a chapter over which is written, "...religious faith alone can confirm our belief as to the existence of a rational soul." ...The object... is to show how metaphysics and religion came to adopt the notion of a soul, and it concludes by saying that true philosophy freely confesses that the... soul is unknown to her. ...Mention is also made of Voltaire's phrase, 'I am body, and I think;' and Lamettrie refers with pleasure to the way in which Voltaire scoffs at the Scholastic proof for the proposition that no matter can think.

Whether the soul occupies only a particular point or a circuit we do not know, but as all nerves do not meet in one point in the brain, the former supposition is improbable. All knowledge is in the soul only at the moment in which it is affected by it; all preservation of it is to be resolved into organic conditions. Thus the 'Natural History of the Soul,' starting from ordinary notions, gradually leads us on into Materialism, and it is concluded that... which feels must also be material. How this comes about Lamettrie too does not know; but why should we (according to Locke) limit the omnipotence of the Creator because of our ignorance? Memory, imagination, passions, and so on, are then explained in a thoroughly materialistic way.

Very ingeniously Lamettrie observes that at bottom I am immediately certain only of my own feeling. That other men also feel, I conclude with very much stronger conviction from the expression of their feelings in gestures and cries than from their articulate speech. That energetic language of the emotions is, however, the same in the animals as in men, and it carries with it much stronger proof than all the sophisms of Descartes. ...[T]he internal organisation of man and of the animals offers a perfect analogy. If it remains for the present incomprehensible how the capability of feeling can be an attribute of matter, it is with this, as with a thousand other puzzles, in which, according to an idea of Leibniz, instead of the thing itself we see only the veil that hides it. ...[S]ensation, like motion, must at all events potentially belong to all matter. So thought the ancients, whose philosophy is preferred by all capable minds to the inadequate attempts of the moderns. After this Lamettrie passes to the doctrine of substantial forms...

The 'Natural History of the Soul' begins by showing that as yet no philosopher, from Aristotle down to Malebranche, had been able to account for the nature of the soul.

In the year 1742 he... received there a position as surgeon to the Guard. In this capacity he made a campaign in Germany, and... was seized by a violent fever, and used this opportunity in order to institute observations upon himself as to the influence of quickened circulation upon thought. He came to the conclusion that thought is nothing but a consequence of the organisation of our mechanism. ...[H]e tried during his convalescence to explain the mental functions by the help of anatomy, and he had his conjectures printed under the title of a 'Natural History of the Soul.' The regimental chaplain sounded the alarm, and soon a universal cry of indignation was raised... His books were recognised as heretical, and he could no longer continue to be surgeon of the Guard. ...about the same time ...writing a satire on his rivals, the foremost Paris practitioners. ...He fled in the year 1746 to Leyden. Here he wrote ...a new satire upon the charlatanism and ignorance of doctors, and soon afterwards (1748) appeared also his 'Homme Machine.'

As a friend, he may have been obliging and self-sacrificing; as an enemy, he was, as in particular had to experience, malicious and low in the choice of his means.

That the true connection could so long be misrepresented is, next to the influence of Hegel and his school, chiefly to be attributed to the resentment excited by Lamettrie's attack upon the Christian morality. People forgot, in consequence, his theoretical writings; and the calmest and most serious of them, including the 'Natural History of the Soul,' were most completely forgotten.

With regard to the questions with which we are concerned, Lamettrie stands at the commencement of the whole series.