Summary: Monadology

Leibniz defines the monad as a simple substance, without parts. The existence of compound bodies proves the existence of monads, since the existence of the compound proves the existence of the simple. As a result, these are the true atoms of nature ¹.

What can these absolutely simple parts, the monads, be like?

In fact, they have neither extent nor figure. Indeed, since extent is divisible, extended bodies are not absolutely simple: similarly, figures are divisible (we can cut, for example, a triangle in two) and can only characterise complex bodies.

Similarly, monads can only appear or disappear all at once (by creation or annihilation): for there is no dissolution to fear for a simple body (only complex bodies can see their parts disjoined) nor formation (one part coming to be added to another to form a whole).

No external movement affects a monad (again, because of their simplicity, the movement most often consisting of a change in the arrangement of the parts between them). As a result, nothing can enter a monad. This leads to the famous idea:

Monads have no windows, through which anything can enter or leave them ².

The monad appears for the moment still as something indeterminate, not even as a kind of void, since this occupies a certain extent.

Leibniz will then try to give content to the monad, without contradicting its simplicity.

It is necessary, first of all, that monads have some qualities, otherwise they would not even be Beings ³.

It is also necessary for monads to be distinguishable from each other; Leibniz referring here to his principle of identity of indiscernibles, stated in his New Essays on Human Understanding following the principle of sufficient reason, according to which there are never in nature two beings which are perfectly one like the other ⁴.

Monads have no parts, but they have qualities.

On the other hand, if no external movement comes to affect the monad, it has internal movements, like all created beings, coming from an internal principle.

Finally, there is in it a plurality of affections and relations, though there are no parts of them ⁵: these are the perceptions.

The Monad is therefore soul. The simple substance that makes up the various bodies is the soul. Indeed, perception cannot be explained according to physical or mechanical bodies alone. This is the meaning of the famous passage:

By pretending that there is a machine whose structure makes one think, feel, have perception, one will be able to conceive it enlarged so that one can enter it as into a mill. And that laid down, when we visit it inside we will only find parts that push each other, and never anything to explain a perception ⁶.

These monads or souls may also be called entelechies, owing to the fact that they have a certain perfection, inasmuch as they are themselves the sources of their internal actions (entelechy is an Aristotelian term that designates a being that has reached its end, hence has attained a certain perfection).

Leibniz notes the importance of memory, which comes to organise perceptions, but which we share with animals (such as the beaten dog that runs away as soon as it sees the stick with which it is used to being hit).

Human being is distinguished from animals by his knowledge of the eternal and necessary truths of Reason.

Two great principles come to direct our reasoning: that of contradiction (is true what is contrary to false) and that of sufficient reason: nothing happens without sufficient reason (or again: there is a reason for everything).

¹ Monadology, 3
² 7
³ 8
⁴ 9
⁵ 13
⁶ 17