Every link of the chain would in that case hang upon another; but there would not be any thing fixed to one end of it, capable of sustaining the whole; and consequently there would be no belief nor evidence.

And this actually is the case with all hypothetical arguments, or reasonings upon a supposition; there being in them, neither any present impression, nor belief of a real existence.
I need not observe, that it is no just objection to the present doctrine, that we can reason upon our past conclusions or principles, without having recourse to those impressions, from which they first arose.

For even supposing these impressions should be entirely effaced from the memory, the conviction they produced may still remain; and it is equally true, that all reasonings concerning causes and effects are originally derived from some impression; in the same manner, as the assurance of a demonstration proceeds always from a comparison of ideas, though it may continue after the comparison is forgot.
SECT.

V.OF THE IMPRESSIONS OF THE SENSES AND MEMORY.
In this kind of reasoning, then, from causation, we employ materials, which are of a mixed and heterogeneous nature, and which, however connected, are yet essentially different from each other.

All our arguments concerning causes and effects consist both of an impression of the memory or, senses, and of the idea of that existence, which produces the object of the impression, or is produced by it.