An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

268 THE THEORY OF INDUCTION
more restricted ; while in Astronomy, Geology, Meteor
ology, we may say that experiment,
as far as we are
concerned, is impossible. We say "as far as we are
concerned," because Nature sometimes produces pheno
mena of so remarkable a character that she may be said
to be making an experiment herself as in an "eclipse
of the sun."
2. What we have said of Experiment introduces us
to the second step towards Explanation, which is to
ascertain the Cause of the fact. This is usually im
possible except by experimental investigation.
We have
to look for the Cause in some fact which precedes (or
accompanies) the one under investigation ; and causal
connections are not given, they have to be discovered.
Mere sequence, as Professor Minto puts it, does not
prove consequence ; to suppose so would be to commit
the fallacy of post hoc ergo propter hoc. The question
is, in the ever-changing succession of events which
Nature presents, what events are causally connected,
in distinction from those which are casually conjoined ?
When do observations of post hoc warrant a conclusion
propter hoc 1 This is decided by varying as much as
possible the circumstances of the phenomenon * under
investigation, so as
casual in them.
to eliminate what is unessential or
In an elementary work it is best to base our account
of the methods of causal investigation on that of J. S.
Mill. Mill elaborated five rules for such investigation,
stating five distinct processes which he called respect
ively the Method of Agreement, the Method of Differ
ence, the Joint Method of Agreement and Difference,
1 The word "phenomenon" ($aiv6iJifvov ) that which appears) is
used synonymously with
that can be observed by our senses.
"
"
fact and "event" to signify anything