f
contiguity and succession. At first sight this seems to serve but little
to my purpose. The reflection on several instances only repeats the
same objects; and therefore can never give rise to a new idea. But upon
farther enquiry I find, that the repetition is not in every particular
the same, but produces a new impression, and by that means the idea,
which I at present examine. For after a frequent repetition, I find,
that upon the appearance of one of the objects, the mind is determined
by custom to consider its usual attendant, and to consider it in a
stronger light upon account of its relation to the first object. It is
this impression, then, or determination, which affords me the idea of
necessity.

I doubt not but these consequences will at first sight be received
without difficulty, as being evident deductions from principles, which
we have already established, and which we have often employed in our
reasonings. This evidence both in the first principles, and in the
deductions, may seduce us unwarily into the conclusion, and make us
imagine it contains nothing extraordinary, nor worthy of our curiosity.
But though such an inadvertence may facilitate the reception of this
reasoning, it will make it be the more easily forgot; for which reason
I think it proper to give warning, that I have just now examined one of
the most sublime questions in philosophy, viz. that concerning the power
and efficacy of causes; where all the sciences seem so much interested.
Such a warning will naturally rouze up the attention of the reader, and
make him desire a more full account of my doctrine, as well as of the
arguments, on which it is founded. This request is so reasonable, that
I cannot refuse complying with it; especially as I am hopeful that these
principles, the more they are examined, will acquire the more force and
evidence.

There is no question, which on account of its importance, as well as
difficulty, has caused more disputes both among antient and modern
philosophers, than this concerning the efficacy of causes, or that
quality which makes them be followed by their effects. But before they
entered upon these disputes, methinks it would not have been improper to
have examined what idea we have of that efficacy, which is the subject
of the controversy. This is what I find principally wanting in their
reasonings, and what I shall here endeavour to supply.

I begin with observing that the terms of EFFICACY, AGENCY, POW