The Method by which the Causes of the Present and Past Conditions of Organic Nature Are to Be Disco | Page 6

apples are sour; and that, so far as it
goes, is a perfect induction. Well, having got your natural law in this
way, when you are offered another apple which you find is hard and
green, you say, "All hard and green apples are sour; this apple is hard
and green, therefore this apple is sour." That train of reasoning is what
logicians call a syllogism, and has all its various parts and terms,--its
major premiss, its minor premiss, and its conclusion. And, by the help
of further reasoning, which, if drawn out, would have to be exhibited in
two or three other syllogisms, you arrive at your final determination, "I
will not have that apple." So that, you see, you have, in the first place,
established a law by Induction, and upon that you have founded a
Deduction, and reasoned out the special conclusion of the particular
case. Well now, suppose, having got your law, that at some time
afterwards, you are discussing the qualities of apples with a friend: you
will say to him, "It is a very curious thing,--but I find that all hard and
green apples are sour!" Your friend says to you, "But how do you know
that?" You at once reply, "Oh, because I have tried it over and over
again, and have always found them to be so." Well. if we were talking
science instead of common sense, we should call that an Experimental
Verification. And, if still opposed, you go further, and say, "I have
heard from the people in Somersetshire and Devonshire, where a large

number of apples are grown, that they have observed the same thing. It
is also found to be the case in Normandy, and in North America. In
short, I find it to be the universal experience of mankind wherever
attention has been directed to the subject." Whereupon, your friend,
unless he is a very unreasonable man, agrees with you, and is
convinced that you are quite right in the conclusion you have drawn.
He believes, although perhaps he does not know he believes it, that the
more extensive Verifications are,--that the more frequently experiments
have been made, and results of the same kind arrived at,--that the more
varied the conditions under which the same results have been attained,
the more certain is the ultimate conclusion, and he disputes the question
no further. He sees that the experiment has been tried under all sorts of
conditions, as to time, place, and people, with the same result; and he
says with you, therefore, that the law you have laid down must be a
good one, and he must believe it.
In science we do the same thing;--the philosopher exercises precisely
the same faculties, though in a much more delicate manner. In scientific
inquiry it becomes a matter of duty to expose a supposed law to every
possible kind of verification, and to take care, moreover, that this is
done intentionally, and not left to a mere accident, as in the case of the
apples. And in science, as in common life, our confidence in a law is in
exact proportion to the absence of variation in the result of our
experimental verifications. For instance, if you let go your grasp of an
article you may have in your hand, it will immediately fall to the
ground. That is a very common verification of one of the best
established laws of nature--that of gravitation. The method by which
men of science establish the existence of that law is exactly the same as
that by which we have established the trivial proposition about the
sourness of hard and green apples. But we believe it in such an
extensive, thorough, and unhesitating manner because the universal
experience of mankind verifies it, and we can verify it ourselves at any
time; and that is the strongest possible foundation on which any natural
law can rest.
So much by way of proof that the method of establishing laws in
science is exactly the same as that pursued in common life. Let us now
turn to another matter (though really it is but another phase of the same
question), and that is, the method by which, from the relations of

certain phenomena, we prove that some stand in the position of causes
towards the others.
I want to put the case clearly before you, and I will therefore show you
what I mean by another familiar example. I will suppose that one of
you, on coming down in the morning to the parlour of your house, finds
that a tea-pot and some spoons which had been left in the room on the
previous evening are gone,--the window is open, and you observe the
mark of a dirty hand on the window-frame, and perhaps, in addition to