Here are some excerpts from Leibniz’s La Monadologie (specifically from Daniel Garber and Roger Arlew’s English translation in Discourse on Metaphysics and Other Essays).
THE MONAD, which we shall discuss here, is nothing but a simple substance that enters into composites – simple, that is, without parts.
Thus, one can say that monads can only begin or end all at once, that is, they can only begin by creation and end by annihilation, whereas composites begin or end through their parts.
The monads have no windows through which something can enter or leave. […] Thus, neither substance nor accident can enter a monad from without.
From this we see that if, in our perceptions, we had nothing distinct or, so to speak, in relief and stronger in flavour, we would always be in a stupor. And this is the state of bare monads.
Thus we attribute action to a monad insofar as it has distinct perceptions, and passion, insofar as it has confused perceptions.
But in simple substances the influence of one monad over another can only be ideal, and can only produce its effect through God’s intervention, when in the ideas of God a monad rightly demands that God take it into account in regulating the others from the beginning of things. For, since a created monad cannot have an internal physical influence upon another, this is the only way in which one can depend on another.
But natural machines, that is, living bodies, are still machines in their least parts, to infinity.
And the author of nature has been able to practice this divine and infinitely marvellous art, because each portion of matter is not only divisible to infinity, as the ancients have recognized, but is also actually subdivided without end, each part divided into parts having some motion of their own;
This we see that each living body has a dominant entelechy, which in the animal is the soul; but the limbs of this living body are full of other living beings, plants, animals, each of which also has its entelechy, or its dominant soul.
That’s a small fraction of the complete essay but it’s clear from these extracts that Leibniz saw both the benefit and the drawback to Object-Oriented Programming, and that they were one and the same.
Objects are indivisible atoms, which cannot mess with each other’s insides nor have their own insides messed with. Rather, they have independent existences, unless one of them sends a message to another via the universal actor willing the two into some correlation.
Something appears to be an object in the first instance, because it is an indivisible thing with its own whole definition and purpose. It is actually both a composite, that can be subdivided into other objects with their own definitions and purposes; and it is a component that contributes toward a larger object that has its own definition and purpose.
Scale-variant analogies can get us out of the problem with the object-as-monad. One that has previously been well-explored is Brad Cox’s Software IC, which sees the object take up a position at only one level of abstraction:
- Component => C instruction.
- Integrated Circuit => Objective-C Object.
- Circuit Board => Package or architectural layer.
- Electronic System => Application.
One that I haven’t yet investigated is the cellular biology analogy introduced by Alan Kay (who also introduced the object-as-monad analogy). He talked about the object as a cell (particularly as a small component of a larger system that has a well-defined boundary across which limited communication occurs), but we can also think about the implications of larger scale order:
- Cell => Object.
- Organ => Object.
- Organism => Object.
- Society => Object.
- Population => Object.
- Biome => Object.
And, as Leibniz said, it’s objects all the way in the other direction: organelles are monads too.