— 665 —
In things which Sense cannot discover, Analogy is the great Rule of Probability.
      §12. The Probabilities we have hitherto mentioned, are only such
as concern matter of fact, and such Things as are capable of Obser-
vation 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 Opera-
tions 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 Load-stone 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 humane Senses, cannot be examined by
them, or be attested by any body, 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 ’tis 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 it
self, we have reason to think, that what we call Heat and Fire,
— 666 —
consists in a violent agitation of the imperceptible minute parts of
the burning matter: Observing likewise that the different refrac-
tions of pellucid Bodies produce in our Eyes the different appear-
ances of several Colours; and also that the different ranging and lay-
ing 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 Arangement and
Refraction of their minute and insensible parts. Thus finding in all
parts of the Creation, that fall under humane Observation, that
there is a gradual connexion of one with another, without any great
or discernable 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 be-
twixt them, we have reason to be perswaded, that by such gentle
steps Things ascend upwards in degrees of Perfection. ’Tis an hard
Matter to say where Sensible and Rational begin, and where In-
sensible 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 remote distance: yet the difference between the
upper and under, where they touch one another, is hardly discern-
able. 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 dif-
ference, that ’twill 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 Per-
fection, 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
— 667 —
leads us often into the discovery of Truths, and useful Productions,
which would otherwise lie concealed.
Locke Hum IV, 16, §12, pp. 665-666-667