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

2/O
THE THEORY OF INDUCTION
investigation have only one circumstance in common,
the circumstance in which alone all the instances agree
is the cause or effect of the given phenomenon." We
may express the rule more simply by saying that facts
which may be eliminated (may be present or absent)
without affecting the event are not causally connected
with it. It is then probable that the remaining fact,
which is present whenever the event occurs, is causally
connected with it. Thus, let A be an event whose
cause is sought for. We observe the circumstances in
which A occurs, in order to find what other facts are
invariably present
with it. Mill indicates distinct facts
by different letters. Suppose, then, that we are able to
analyse :
the various instances of A as follows first
instance, Abed; second, A c f e ; third, A g h c ;
and so on. Then c is the only other fact in which the
instances of A agree ; hence there is a probability that
A and c are causally connected. The principle of the
Method is the same whether b, c, d, &c., come before or
after A or are simultaneous with it.
Mill s statement of this method ignores a preliminary
difficulty. Nature not only fails to show us, at a glance,
what events are really connected with a given one ; she
does not give us events marked off into distinct and
separate phenomena. To denote the facts learnt through
observation by letters a, b, c, &c., is to take for granted
that the hardest part of the work of observation is already
done. When phenomena have been analysed into their
elements in this manner, it is a very simple
affair to
ascertain the common facts in the different instances.
We must not forget that the Method of Single Agreement
starts with prepared material, taking for granted the
very thing that is most difficult to discern. This is why
it is so difficult to be sure that the instances have only