# Hume's definition of cause and effect

Hume remarks that we may define the relation of cause and effect such that ``where, if the first object had not been, the second never had existed."

I do not understand this. Let's say A causes B. Then it does not necessarily mean A is the only cause of B. If C also causes B, it is possible that A has not happened but B has happened because C has happened AND "A causes B" is still a true sentence.

It seems more logical to say "if the second object (effect) did not exist the first object (cause) never had existed".

Hume is talking about concrete events. You are talking about possible events.

For example, a bus being late may be caused by 1) a car crash or 2) the driver not showing up. Suppose for the moment that it is not possible for these events to happen simultaneously.

Now let's look at bus nr. 609 which should have arrived at my station as of August 8, 2015, 11:50 CET, but failed. This is a concrete event. It is either caused by a car crash or by the driver not showing up. That is what Hume is talking about. If the cause of the bus arriving late hadn't been there, it would have been on time.

Of course, that doesn't mean the other cause (which wasn't the cause for this bus arriving late) can never cause any other bus to arrive late. But for this concrete event, there is only one cause.

• so can we assume here a cause - for a concrete event (effect) - can be made up of one or more events – kiyarash Aug 8 '15 at 10:22
• @kiyarash no, not in Hume, but an effect may be caused by multiple causes. This would be the case of the non-existence of any of the causes would cause the effect to be non-existent. This is the case if A and B cause C only if they both occur. – Keelan Aug 8 '15 at 10:24

How to interpret the quote “where, if the first object had not been, the second never had existed."?

1) Literally the quote says: The first object A is necessary for the second object B. Spelled out in logical terms: NOT A implies NOT B. This means B => A. (Note the orientation of the implication).

2) A second interpretation says: The first object is necessary and sufficient for the second object. Spelled out in logical terms: B => A AND A => B, which is A <=> B (equivalence)

3) But possibly Hume says: A causes B means “The existence of A implies the existence of B”. Then the existence of A is sufficient for the existence of B, logically A => B.

Therefore: Would you please name the original passage from Hume.

• An Enquiry concerning Human Understanding. Sec. VII. – kiyarash Aug 10 '15 at 7:46
• The citation from your post has been added in the later edition K from 1753/54. It is alternative 1) from my answer. - Earlier editions read only: "we may define a cause to be an object, followed by another, and where all the objects similar to the first are followed by objects similar to the second". This phrase suggests alternative 3), in particular when considering the context of section VII. - Hence either Hume does not know the difference between necessary and sufficient conditions or Hume considers only monocausal relations? I prefer the latter view. – Jo Wehler Aug 10 '15 at 14:33