Causation

Philosophers have theorized about causation since well before Aristotle, who distinguished several types of causation: efficient, material, final, and formal. For example, a wood carving is made by an artist (the efficient cause) by chiseling a piece of wood (the material cause) for the purpose of creating a beautiful object (the final cause), arriving at something that has the properties of a wood carving (the formal cause).

Although Aristotle's typology framed discussions of causation until the scientific revolution and in some circles even until David Hume, the focus settled onto analyzing efficient causation and in particular on understanding the kinds of substances that might interact causally. René Descartes, for example, separated material and mental substances and wrote extensively on how cross-substance causation might happen. Discussions of causation thus became entangled with the metaphysics of substance, and positions ranged all the way from Baruch Spinoza, who claimed there is only one type of substance, to Gottfried Wilhelm Leibniz, who claimed there was an infinity of unique substances, one per monad. Everyone wanted to understand causation as involving some "power" to produce change, and different substances possess different sorts of powers over their own and other substances. For example, the empiricist Bishop George Berkeley argued that our ideas (sensations) cannot be caused by other ideas or matter, because ideas and matter are "inert" and do not have the sort of causal "power" necessary for efficient causation. Only an agent like God or a willful person possesses such power. John Locke, in An Essay concerning Human Understanding, wrote voluminously trying to explicate the idea of causal power in empiricist terms. David Hume, the brilliant eighteenth-century Scottish philosopher, finally rejected the notion of causal power as being beyond direct observation, and he recast the problem of understanding the connection between a cause and its effect as another version of the problem of induction. Although causes always seem to be followed by their effects, the bond between them might well be nothing more than a psychological habit we develop as a result of regularly perceiving the idea of one type of object or event (e.g., thunder) just after the idea of another (e.g., lightning). Hume's challenge was to find compelling reasons for believing that when an object similar to one we have seen previously occurs, then the effect must necessarily occur. No one has succeeded in answering Hume's challenge, but his effect on the debate was as powerful as Aristotle's. All modern theories of causation begin with something like Hume's story: there are objects or events that we can group as similar, like the events of walking in the rain with no coat and developing a cold. They all ask what does it mean to assert that the relation between these events is causal.