Notes on Hume's Treatise
by G. J. Mattey
PART III. OF KNOWLEDGE AND PROBABILITY
§ III. Why a cause is always necessary.
This is in answer to the first question, i.e., why we claim that whatever has a beginning of existence has a cause.
Hume observes that "'Tis a general maxim in philosophy, that whatever begins to exist, must have a cause of existence." This is used in our reasoning without proof, as it is taken as intuitive; however, there is in it "no mark of any such intuitive certainty." Quite the contrary.
Certainty is confined to comparisons of ideas present to the mind (see Section I for the four relations admitting of such comparison). These are not "imply'd in" the maxim, so it is not intuitively certain, unless another kind of relation can be found.
In fact, the maxim is neither intuitively nor demonstratively certain, so whether we can find the other relation is moot. For we can conceive of an object non-existent at one moment and existent at the next. The ideas of cause and beginning of existence are distinct and hence separable (according to Hume's principle that whatever is distinguishable in thought is separable in existence). There is no contradiction in the imagining of such a thing, so there is no demonstration of the necessity of the maxim.
Some fallacious demonstrations are given.
Hobbes: without a cause, there would be nothing to determine the existence of anything at a specific time, all times being alike. But both the that and the when or where stand or fall on the same footing. It is no more absurd to say that without a cause a thing begins to exist at a time and place like all others, then it is absurd to say that without a cause a thing begins to exist at all. Both depend on the same reasoning, so the absurdity of the first cannot prove the absurdity of the second.
Clarke: What lacks a cause would produce itself, hence "exist before it existed; which is impossible." But this begs the question: in denying that there is a cause, we grant that there must be one, namely, the object itself. The allegedly absurd hypothesis, that the object had no cause, excludes the thing itself.
Locke: What lacks a cause is produced by nothing, but nothing produces nothing. But this depends on the same fallacy [begging the question: it is assumed not to be produced, yet is produced by nothing].
If everything has a cause, then if the cause is not something else it is either itself or nothing. But that is what is in question.
A worse argument: the idea of cause is implied in that of effect. This says nothing about whether a beginning of existence is an effect.
So, the maxim is not based on "knowledge or any scientific reasoning." The only remaining source is observation and experience. So how does experience give rise to such a maxim? It will be "convenient" to "sink this question in" the particular case, i.e., " Why we conclude, that such particular causes must necessarily have such particular effects, and why we form an inference from one to another." The answer to this may answer the previous question.