Again, when I consider the influence of this constant conjunction, I perceive, that such a relation can never be an object of reasoning, and can never operate upon the mind, but by means of custom, which determines the imagination to make a transition from the idea of one object to that of its usual attendant, and from the impression of one to a more lively idea of the other.

However extraordinary these sentiments may appear, I think it fruitless to trouble myself with any farther enquiry or reasoning upon the subject, but shall repose myself on them as on established maxims.
It will only be proper, before we leave this subject, to draw some corrollaries from it, by which we may remove several prejudices and popular errors, that have very much prevailed in philosophy.

First, We may learn from the foregoing, doctrine, that all causes are of the same kind, and that in particular there is no foundation for that distinction, which we sometimes make betwixt efficient causes and causes sine qua non; or betwixt efficient causes, and formal, and material, and exemplary, and final causes.

For as our idea of efficiency is derived from the constant conjunction of two objects, wherever this is observed, the cause is efficient; and where it is not, there can never be a cause of any kind.

For the same reason we must reject the distinction betwixt cause and occasion, when supposed to signify any thing essentially different from each other.