The soul and how it is united to the body and receives its ideas.

Newton was persuaded that the soul is an incomprehensible substance.

Several people who knew Locke have assured me that Newton confessed to Locke that we do not have enough knowledge of nature to assert that it is impossible for God to add the gift of thought to any extended being whatsoever.

The great difficulty is rather to know how any being can think, than to know how matter can become thinking.

Thought has nothing in common with the attributes in the extended being called “body”.

But do we know all the properties of bodies?

It seems a bold to say to God: You were able to give movement, gravitation, vegetation, and life to a being, but you cannot give it thought!*

Some say that if matter could have thought, then the soul would not be immortal.

This is not consistent reasoning.

Is it more difficult for God to preserve than to create?

If an indivisible atom endures eternally, why would the gift of thinking in it not endure as long as the atom itself? If I am not mistaken, those who refuse to God the power of joining ideas to matter are obliged to say that what we call spirit is a being whose very essence is to think, to the exclusion of all extended beings.

But if it is of the nature of spirit to think essentially, then it thinks necessarily, and it always thinks, just as every triangle necessarily and always has three angles, independently of God.

What! As soon as God creates something that is not matter, must that something necessarily think? Weak and bold as we are! Do we know if God has not formed millions of beings that have neither the properties of spirit nor those of matter as we know them? We are like a shepherd who, having only ever seen oxen, would say: “If God wants to make other animals, they must have horns and chew the cud.”

So which is more respectful toward the Divinity: to affirm that there are beings that have, without Him, the divine attribute of thought—or to suppose that God can grant this attribute to whatever being He deigns to choose?

From this alone one sees how unjust are those who wanted to make of Locke’s sentiment a crime, and who maliciously fought, with the weapons of religion, an idea that was purely philosophical.

In any case, Newton was far from venturing a definition of the soul, as so many others dared to do. He believed it possible that there might be millions of other thinking substances whose nature could be entirely different from the nature of our soul. Thus, the division that some have made of all nature between “body” and “spirit” seems like the definition of a deaf and blind man who, defining the senses, would suspect neither sight nor hearing: by what right, indeed, could one say that God has not filled immense space with an infinity of substances that have nothing in common with us?

Newton made no system about how the soul is united to the body, or how ideas are formed. An enemy of systems, he judged nothing except by analysis; and when that light failed him, he knew how to stop.

There have so far been in the world four opinions on the formation of ideas:

The first is that of almost all the ancient nations who, imagining nothing beyond matter, regarded our ideas in our mind as the impression of a seal upon wax. This confused opinion was more a crude instinct than a reasoning; the philosophers who later wanted to prove that matter thinks by itself strayed even further—for the common people were mistaken without reasoning, but those philosophers erred by principle; none of them could ever find anything in matter that could prove it has intelligence by itself.

Locke appears to be the only one who removed the contradiction between matter and thought by appealing at once to the creator of all thought and all matter, and modestly saying: He who can do everything—can He not make a material being, an atom, an element of matter think?

He held only to this possibility, as a wise man should: to affirm that matter actually thinks because God could communicate this gift would be the height of rashness; but is it less bold to affirm the contrary?

The second opinion, and the most generally received, is that which, establishing soul and body as two beings that have nothing in common, nevertheless affirms that God created them to act on one another.

The only proof we have of this action is the experience each of us believes we have: we experience that our body sometimes obeys our will, sometimes masters it; we imagine they act on one another because we feel it, and it is impossible for us to pursue the inquiry further.

An objection is made to this system which seems unanswerable: if an external object, for example, communicates a vibration to our nerves, that movement either goes to our soul or it does not. If it does, it communicates movement to the soul—which would suppose the soul to be corporeal; if it does not, then there is no action at all.

All that can be answered is that this action is one of those things whose mechanism will always remain unknown: a sad way to conclude, but almost the only one fitting to man on more than one point of metaphysics.

The third system is that of Descartes’ “occasional causes,” carried further by Malebranche.

It begins by supposing that the soul cannot have any influence on the body, and from there it advances too far: for from the fact that the influence of the soul on the body cannot be conceived, it does not at all follow that it is impossible.

It then supposes that matter, as an occasional cause, impresses itself upon our body, and that then God produces an idea in our soul; and conversely, when man produces an act of will, God acts immediately on the body in consequence of that will.

Thus, man acts and thinks only in God; which, it seems to me, can have no clear meaning except by saying that God alone acts and thinks for us.

The difficulties arising from this hypothesis are crushing: for how, in this system, can man will by himself, and yet not think by himself?

If God has not given us the faculty of producing movement and ideas, if He alone acts and thinks, then He alone wills. Not only are we no longer free, but we are nothing—or rather, we are modifications of God Himself.

In this case there is no soul, no intelligence in man; and there is no point in explaining the union of body and soul, since it does not exist, and since God alone exists.

The fourth opinion is that of Leibniz’s pre-established harmony.

In his hypothesis the soul has no commerce with its body: they are two clocks made by God, each with its own spring, which run for a certain time in perfect correspondence: one shows the hours, the other strikes them.

The clock which shows the hour does not do so because the other strikes; but God has arranged their movement so that the hand and the striking always correspond.

Thus the soul of Virgil produced the Aeneid, and his hand wrote the Aeneid without that hand obeying in any way the intention of the author; but God had arranged from all eternity that the soul of Virgil would compose verses, and that a hand attached to the body of Virgil would write them down.

Leaving aside the extreme difficulty of reconciling free will with this pre-established harmony, there is a strong objection: if, according to Leibniz, nothing happens without a sufficient reason drawn from the very nature of things, what reason did God have to unite two incommensurable beings—two beings so heterogeneous, so infinitely different as soul and body—and of which one has no influence on the other?

Might as well have placed my soul in Saturn as in my body: the union of soul and body becomes, in this view, a very superfluous thing.

But the rest of Leibniz’s system is even more extraordinary: one can see its foundations in the Supplement to the Acts of Leipzig, vol. VII, and consult the commentaries several Germans have made on it with a wholly geometric method.

According to Leibniz, there are four kinds of simple beings, which he calls monads (as will be seen in Chapter VIII); here we speak only of the kind of monad called “our soul.”

The soul, he says, is a concentration, a living mirror of the whole universe, which has within itself all the confused ideas of all the modifications of this world, present, past, and future.

Newton, Locke, and Clarke, when they heard of such an opinion, expressed for it as much scorn as if Leibniz had not been its author; but since very great German philosophers have gloried in explaining what no Englishman ever wanted to hear, I am obliged to set out clearly this hypothesis of the famous Leibniz, which has become more respectable to me since you made it the object of your research.

Every created simple being, he says, is subject to change—otherwise it would be God: the soul is a simple created being; therefore it cannot remain in the same state.

But bodies, being composite, can produce no alteration in a simple being: its changes must therefore arise from its own nature.

Its changes are thus the successive ideas of the things of this universe: it has some clear ones; but all the things of this universe, says Leibniz, are so dependent on one another, so forever linked, that if the soul has a clear idea of one of these things, it necessarily has confused and obscure ideas of all the rest.

One might, to clarify this opinion, give the example of a man who has a clear idea of a game; he has at the same time several confused ideas of several combinations of this game. A man who has at the moment a clear idea of a triangle has an idea of several properties of the triangle, which may present themselves in turn more clearly to his mind.

This is how the monad of man is a living mirror of this universe.

It is easy to answer such a hypothesis by saying that, if God has made the soul a mirror, He has made it a very dull mirror—and that, if there are no other reasons for advancing such strange suppositions than this supposed indispensable connection of all the things of this world, one is building this bold edifice on foundations scarcely visible.

For when we have a clear idea of the triangle, it is because we have knowledge of the essential properties of the triangle; and if the ideas of all these properties do not all at once present themselves vividly to our mind, they are there nevertheless—they are contained in this clear idea, because they are necessarily related to one another.

But is the whole assemblage of the universe in this case?

If you take away one property from the triangle, you take away everything; but if you remove a grain of sand from the universe, will the rest be entirely changed?

If out of a hundred million beings linked two by two, the first two change places with each other, do the others necessarily change places? Do they not retain their relations among themselves?

Moreover, do a man’s ideas have among themselves the same chain that one supposes in the things of this world?

What link, what necessary bridge is there between the idea of the night and the unknown objects I see when I wake up?

What chain is there between the temporary death of the soul in a deep sleep or in a faint, and the ideas one receives upon recovering consciousness?

Even if it were possible that God had done everything Leibniz imagines, must we believe it on a mere possibility?

What has he proved by all these new efforts? That he had a very great genius; but did he enlighten himself, and did he enlighten others?

Strange thing! We do not know how the earth produces a blade of grass, how a woman makes a child—and we think we know how we form ideas!

If one wants to know what Newton thought of the soul, and of the manner in which it operates, and which of all these opinions he embraced, I will answer that he followed none.

What then did he know about this matter—he who had subjected infinity to calculation and discovered the laws of gravitation?

He knew how to doubt.