Summary: Monadology

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

What, then, are these absolutely simple entities, the monads?

They possess neither extension nor shape. Since extension is divisible, extended bodies are not absolutely simple. Similarly, shapes are divisible — a triangle, for instance, can be bisected — and can only characterise complex bodies.

Likewise, monads can only appear or disappear all at once — through creation or annihilation — for a simple substance has nothing that can dissolve. Only compound bodies can have their parts disjoined, just as only composite structures can be formed by the joining of one part to another.

No external change can affect a monad — for, by virtue of their simplicity, change typically involves a rearrangement of parts. Consequently, nothing can enter a monad. This leads to the famous assertion:

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

At this stage, the monad still appears as something entirely indeterminate — not even a kind of void, since even a void occupies a certain extension.

Leibniz then seeks 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.

Monads must also be distinguishable from one another. Here, Leibniz refers to his principle of identity of indiscernibles, stated in his New Essays on Human Understanding and derived from 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, yet they do possess qualities.

While no external change can affect a monad, it does undergo internal changes, like all created beings, arising from an internal principle.

Finally, within the monad there is a plurality of affections and relations, though there are no parts of them ⁵. These are what Leibniz calls perceptions.

The monad is therefore a soul. The simple substance underlying all bodies is, in essence, a soul. Indeed, perception cannot be explained by purely physical or mechanical means. This is the point of the famous passage:

Imagine a machine constructed in such a way as to think, feel, and perceive. Now, suppose it were enlarged to a scale that allowed us to step inside it, like entering a mill. Upon inspecting its interior, we would find only parts pushing against one another — never anything to explain a perception ⁶.

These monads, or souls, may also be called entelechies, by virtue of possessing a certain perfection, inasmuch as they are the sources of their own internal actions. (The term 'entelechy' comes from Aristotle and refers to a being that has reached its end, thereby attaining a certain degree of perfection.)

Leibniz underlines the importance of memory, which organises our perceptions — something we share with animals. For instance, a beaten dog will flee at the sight of the stick that was used to strike it.

Human beings are distinguished from animals by their knowledge of the eternal and necessary truths of Reason.

Two great principles guide our reasoning: that of contradiction (which states that what contradicts the false is true) and that of sufficient reason: nothing occurs without a sufficient reason — in other words, there is a reason for everything.

¹ Monadology, 3
² 7
³ 8
⁴ 9
⁵ 13
⁶ 17