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

THE GENERAL NATURE OF INDUCTION. 227
sequent; looked at in its reference to the real world,
it states that M is the cause of P it
; implies that we
have discovered a law of causation in Nature, and M
is the cause in question. Now when the syllogism is
changed from the hypothetical to the categorical form,
M becomes the middle term :
Hypothetical. Categorical
If anything is M it is P, All M is P,
S is M ; S is M ;
/. S is P. /. S is P.
Hence Aristotle says TO fjiev yap alnov TO pecrov (An.
Post., ii. 2) :
"
the middle term expresses the cause."
We may therefore say with Ueberweg (Logic, 101):
the worth of the syllogism as a form of knowledge
depends on the assumption that general laws of causa
tion hold in Nature, and may be known. And that
syllogism has the greatest scientific value in which the
mediating concept (the middle term), by which we
know the truth of the conclusion, expresses the real
cause of the fact stated in the conclusion.
This is verified in each of the above examples. In
(i) the middle concept is the lengthening of the pen
dulum; and this is the real cause of the lengthening
of its path. In (2) the middle concept is that of
motion round a centre ; and such motion is the cause
which generates the centrifugal tendency. In (3) the
middle concept is the increase in the speed of the
motion round a centre; and this increase causes an
increase in the centrifugal tendency.
Aristotle was aware that the middle term does not
always express the real case. In the following, the
middle is not the cause :
"
Whatever is near, does not
twinkle; planets are near, therefore they do not