12. In things which sense cannot discover, analogy is the great rule of probability.
[Secondly], The probabilities
we have hitherto mentioned are only such as concern matter of fact, and such things as are capable of observation
and testimony. There remains that other sort, concerning which men entertain opinions with variety of assent,
though the things be such, that falling not under the reach of our senses, they are not capable of testimony. Such
are, 1. The existence, nature and operations of finite immaterial beings without us; as spirits, angels, devils, etc.
Or the existence of material beings which, either for their smallness in themselves or remoteness from us, our
senses cannot take notice of--as, whether there be any plants, animals, and intelligent inhabitants in the planets,
and other mansions of the vast universe. 2. Concerning the manner of operation in most parts of the works of
nature: wherein, though we see the sensible effects, yet their causes are unknown, and we perceive not the ways
and manner how they are produced. We see animals are generated, nourished, and move; the loadstone draws
iron; and the parts of a candle, successively melting, turn into flame, and give us both light and heat. These and
the like effects we see and know: but the causes that operate, and the manner they are produced in, we can only
guess and probably conjecture. For these and the like, coming not within the scrutiny of human senses, cannot be
examined by them, or be attested by anybody; and therefore can appear more or less probable, only as they more
or less agree to truths that are established in our minds, and as they hold proportion to other parts of our
knowledge and observation. Analogy in these matters is the only help we have, and it is from that alone we draw
all our grounds of probability. Thus, observing that the bare rubbing of two bodies violently one upon another,
produces heat, and very often fire itself, we have reason to think, that what we call heat and fire consists in a
violent agitation of the imperceptible minute parts of the burning matter. Observing likewise that the different
refractions of pellucid bodies produce in our eyes the different appearances of several colours; and also, that the
different ranging and laying the superficial parts of several bodies, as of velvet, watered silk, etc., does the like,
we think it probable that the colour and shining of bodies is in them nothing but the different arrangement and
refraction of their minute and insensible parts. Thus, finding in all parts of the creation, that fall under human
observation, that there is a gradual connexion of one with another, without any great or discernible gaps between,
in all that great variety of things we see in the world, which are so closely linked together, that, in the several
ranks of beings, it is not easy to discover the bounds betwixt them; we have reason to be persuaded that, by such
gentle steps, things ascend upwards in degrees of perfection. It is a hard matter to say where sensible and rational
begin, and where insensible and irrational end: and who is there quick-sighted enough to determine precisely
which is the lowest species of living things, and which the first of those which have no life? Things, as far as we
can observe, lessen and augment, as the quantity does in a regular cone; where, though there be a manifest odds
betwixt the bigness of the diameter at a remote distance, yet the difference between the upper and under, where
they touch one another, is hardly discernible. The difference is exceeding great between some men and some
animals: but if we will compare the understanding and abilities of some men and some brutes, we shall find so
little difference, that it will be hard to say, that that of the man is either clearer or larger. Observing, I say, such
gradual and gentle descents downwards in those parts of the creation that are beneath man, the rule of analogy
may make it probable, that it is so also in things above us and our observation; and that there are several ranks of
intelligent beings, excelling us in several degrees of perfection, ascending upwards towards the infinite perfection
of the Creator, by gentle steps and differences, that are every one at no great distance from the next to it. This sort
of probability, which is the best conduct of rational experiments, and the rise of hypothesis, has also its use and
influence; and a wary reasoning from analogy leads us often into the discovery of truths and useful productions,
which would otherwise lie concealed.
