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a certain way. But what if we decided that Hume is wrong? What if we said that “the reason causes produce their effects in the case of the billiard balls is that the cue-ball transfers its motion to the ball it hits”? The problem with this, however, is that, as Gottfried Leibniz (1646-1716) shows us, this concept of transferring motion is just as problematic as the alleged necessary connection. Leibniz, one of the inventors of calculus and a contributor to the scientific revolution of the seventeenth century, argued that the concept of causation between distinct substances is incoherent.

Since Aristotle, one of the fundamental philosophical and scientific concepts has been “substance.” To be a substance is to be a thing with properties. For example, we might describe Yoda as a substance because he is a thing that has properties, such as being old and green, and a thing that moves, talks, is conscious, has a body, and is capable of moral reasoning. These properties depend on the existence of a thing which has them. If the substance of Yoda were annihilated, then there would be nothing to have these “Yoda” properties; there must be something to be old, green, in motion, conscious, and so on. So substances are things that have properties, and properties depend on substances for their existence.

According to Leibniz, the concept of causation includes the transfer of motion or other properties from one substance (a cue-ball) to another substance (a two-ball). This means that causation is a kind of giving. So, in addition to the concept of substance, we need the further concept of causation as giving. We often think of a cause as an object giving its own properties to another object—the particles in a lightsaber give some of their motion to the particles of metal in a blast-door causing it to heat up. It follows then that causes must have the properties they give to their effects; a lightsaber cannot cause a blast-door to be hot unless it has heat itself.

Now, as Leibniz argues in his Monadology, one body cannot cause a change in another:

There is also no way of explaining how a [substance] can be altered or changed internally by some other creature . . . [Properties] cannot be detached, nor can they go about outside of substances . . . Thus, neither substance nor [properties] can enter a [substance] from without. 99

If one physical object, say a cue-ball, were to have a property, say motion, and if that cue-ball were to cause motion in a (presently) stationary eight-ball, then the cue-ball would have to transfer some of its motion to the eight-ball. But how does one substance transfer one of its own properties to another substance? As we’ve said, since properties are properties of something—they’re not free-floating, but attached to substances—then the property of motion can’t be given from the cue-ball to the eight-ball without some part of the cue-ball’s substance moving from the cue-ball to the eight-ball as well. But this doesn’t happen; bodies don’t cause motion in other bodies by giving up part of themselves. When Luke causes C-3PO to rise in the air, he doesn’t transfer any of his own substance to C-3PO’s chair. So causation as the giving of properties from one body to another, Leibniz argues, can’t happen.

The Force, however, is not this kind of causation. When a Jedi knocks over a line of battle droids, he doesn’t transfer some of his motion to the droids. And certainly we don’t think that all causation includes the transfer of properties in this way. What’s being given to the glass by the diamond that cuts it? What property of the earth is given to the falling body? But if we reject this model of causation, then we’re stuck with the problem of figuring out exactly what all instances of causation have in common, by virtue of which they are causes.

“There’s [Not] One All-Powerful Force Controlling Everything”

If Hume is right, we have no knowledge of causation because we lack any observations of the main component of causes: the necessary connection between the cause and the effect. And if the account