for the observation of such imperfect understandings; since it may well
employ the utmost care and attention of a philosophic genius to discover
and observe them. Animals, therefore, are not guided in these inferences
by reasoning: Neither are children: Neither are the generality of
mankind, in their ordinary actions and conclusions: Neither are
philosophers themselves, who, in all the active parts of life, are, in
the main, the same with the vulgar, and are governed by the same maxims.
Nature must have provided some other principle, of more ready, and more
general use and application; nor can an operation of such immense
consequence in life, as that of inferring effects from causes, be
trusted to the uncertain process of reasoning and argumentation. Were
this doubtful with regard to men, it seems to admit of no question with
regard to the brute creation; and the conclusion being once firmly
established in the one, we have a strong presumption, from all the rules
of analogy, that it ought to be universally admitted, without any
exception or reserve. It is custom alone, which engages animals, from
every object, that strikes their senses, to infer its usual attendant,
and carries their imagination, from the appearance of the one, to
conceive the other, in that particular manner, which we denominate
_belief_. No other explication can be given of this operation, in all
the higher, as well as lower classes of sensitive beings, which fall
under our notice and observation [19].

[19] Since all reasonings concerning facts or causes is derived
merely from custom, it may be asked how it happens, that men so
much surpass animals in reasoning, and one man so much
surpasses another? Has not the same custom the same
influence on all?

We shall here endeavour briefly to explain the great difference