Causal Reasoning

Aristotle‘s enumerative induction was a way of acquiring knowledge about what substances belong in what categories. In a Newtonian world in which there is only one material substance, induction is instead used for discovering connections between events. We assume that causal connections don’t exist between types of events that follow each other only once. There must be what philosopher David Hume called Constant Conjunction. Because dynamite explodes essentially every time you touch a match to it, we say that the match causes the explosion. We come to this conclusion by the same kind of inductive reasoning that prompts us to say all crows are black, but the conclusion itself is about a connection between events in a causal network, not about a substance. We could, of course, say that dynamite is an explosive substance if we wished. But we can also use this connection between events to understand general laws about combustion, and build things like internal combustion engines using those general laws.

This ‘Constant Conjunction’ doesn’t have to be an explosion that occurs every possible time the match touches the dynamite. There will be no explosion if the two touch each other under water, for example. Nor is constant conjunction sufficient to define a causal connection, even if it is necessary. Some events are constantly conjoined because they are connected to a third event which is the real causal factor. An alarm system in a factory will go off just before an explosion, but that doesn’t mean the alarm sound caused the explosion. Both the alarm and the explosion were caused by a…