RULES BY WHICH TO JUDGE OF CAUSES AND EFFECTS.
According to the precedent doctrine, there are no objects which, by the
mere survey, without consulting experience, we can determine to be the
causes of any other; and no objects which we can certainly determine in
the same manner not to be the causes. Any thing may produce any thing.
Creation, annihilation, motion, reason, volition; all these may arise
from one another, or from any other object we can imagine. Nor will
this appear strange if we compare two principles explained above, _that
the constant conjunction of objects determines their causation_,[18]
and _that, properly speaking, no objects are contrary to each other
but existence and non-existence_. Where objects are not contrary,
nothing hinders them from having that constant conjunction on which the
relation of cause and effect totally depends.
Since, therefore, 'tis possible for all objects to become causes or
effects to each other, it may be proper to fix some general rules by
which we may know when they really are so.
1. The cause and effect must be contiguous in space and time.
2. The cause must be prior to the effect.
3. There must be a constant union betwixt the cause and effect. 'Tis
chiefly this quality that constitutes the relation.
4. The same cause always produces the same effect, and the same effect
never arises but from the same cause. This principle we derive from
experience, and is the source of most of our philosophical reasonings.
For when by any clear experiment we have discovered the causes or
effects of any phenomenon, we immediately extend our observation to
every phenomenon of the same kind, without waiting for that constant
repetition, from which the first idea of this relation is derived.
5. There is another principle which hangs upon this, viz. that where
several different objects produce the same effect, it must be by means
of some quality which we discover to be common amongst them. For as
like effects imply like causes, we must always ascribe the causation to
the circumstance wherein we discover the resemblance.
6. The following principle is founded on the same reason. The
difference in the effects of two resembling objects must proceed from
that particular in which they differ. For as like causes always
produce like effects, when in any instance we find our expectation to
be disappointed, we must conclude that this irregularity proceeds from
some difference in the causes.
7. When any object increases or diminishes with the increase or
diminution of its cause, 'tis to be regarded as a compounded effect,
derived from the union of the several different effects which arise
from the several different parts of the cause. The absence or presence
of one part of the cause is here supposed to be always attended with
the absence or presence of a proportionable part of the effect. This
constant conjunction sufficiently proves that the one part is the cause
of the other. We must, however, beware not to draw such a conclusion
from a few experiments. A certain degree of heat gives pleasure; if you
diminish that heat, the pleasure diminishes; but it does not follow,
that if you augment it beyond a certain degree, the pleasure will
likewise augment; for we find that it degenerates into pain.
8. The eighth and last rule I shall take notice of is, that an object,
which exists for any time in its full perfection without any effect, is
not the sole cause of that effect, but requires to be assisted by some
other principle, which may forward its influence and operation. For as
like effects necessarily follow from like causes, and in a contiguous
time and place, their separation for a moment shows that these causes
are not complete ones.
Here is all the _logic_ I think proper to employ in my reasoning;
and perhaps even this was not very necessary, but might have been
supplied by the natural principles of our understanding. Our scholastic
headpieces and logicians show no such superiority above the mere
vulgar in their reason and ability, as to give us any inclination
to imitate them in delivering a long system of rules and precepts
to direct our judgment in philosophy. All the rules of this nature
are very easy in their invention, but extremely difficult in their
application; and even experimental philosophy, which seems the most
natural and simple of any, requires the utmost stretch of human
judgment. There is no phenomenon in nature but what is compounded
and modified by so many different circumstances, that, in order to
arrive at the decisive point, we must carefully separate whatever is
superfluous, and inquire, by new experiments, if every particular
circumstance of the first experiment was essential to it. These new
experiments are liable to a discussion of the same kind; so that the
utmost constancy is required to make us persevere in our inquiry,
and the utmost sagacity to chuse the right way among so many that
present themselves. If this be the case even in natural philosophy,
how much more in moral, where there is a much greater complication
of circumstances, and where those views and sentiments, which are
essential to any action of the mind, are so implicit and obscure,
that they often escape our strictest attention, and are not only
unaccountable in their causes, but even unknown in their existence? I
am much afraid, lest the small success I meet with in my inquiries,
will make this observation bear the air of an apology rather than of
boasting.
If any thing can give me security in this particular, 'twill be the
enlarging the sphere of my experiments as much as possible; for which
reason, it may be proper, in this place, to examine the reasoning
faculty of brutes, as well as that of human creatures.
[18] Part I. Sect 5.