that again from another testimony, by a
visible gradation, it will we arrive at those who were eyewitnesses and
spectators of the event. It is obvious all this chain of argument or
connexion of causes and effects, is at first founded on those characters
or letters, which are seen or remembered, and that without the authority
either of the memory or senses our whole reasoning would be chimerical
and without foundation. 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. Here therefore
we have three things to explain, viz. First, The original impression.
Secondly, The transition to the idea of the connected cause or effect.
Thirdly, The nature and qualities of that idea.

As to those impressions, which arise from the senses, their ultimate
cause is, in my opinion, perfectly inexplicable by human reason, and it
will always be impossible to decide with certainty, whether they arise
immediately from the object, or are produced by the creative power of
the mind, or are derived from the author of our being. Nor is such a
question any wa