common theory of the syllogism
evidently throwing no light upon it. My practice (learnt from Hobbes and
my father) being to study abstract principles by means of the best
concrete instances I could find, the Composition of Forces, in dynamics,
occurred to me as the most complete example of the logical process I was
investigating. On examining, accordingly, what the mind does when it
applies the principle of the Composition of Forces, I found that it
performs a simple act of addition. It adds the separate effect of the
one force to the separate effect of the other, and puts down the sum of
these separate effects as the joint effect. But is this a legitimate
process? In dynamics, and in all the mathematical branches of physics,
it is; but in some other cases, as in chemistry, it is not; and I then
recollected that something not unlike this was pointed out as one of the
distinctions between chemical and mechanical phenomena, in the
introduction to that favourite of my boyhood, Thompson's _System of
Chemistry_. This distinction at once made my mind clear as to what was
perplexing me in respect to the philosophy of politics. I now saw, that
a science is either deductive or experimental, according as, in the
province it deals with, the effects of causes when conjoined, are or are
not the sums of the effects which the same causes produce when separate.
It followed that politics must be a deductive science. It thus appeared,
that both Macaulay and my father were wrong; the one in assimilating the
method of philosophizing in politics to the purely experimental method
of chemistry; while the other, though right in adopting a deductive
method, had made a wrong selection of one, having taken as the type of
deduction, not the appropriate process, that of the deductive branches
of natural philosophy, but the inappropriate one of pure geometry,
which, not being a science of causation at all, does not require or
admit of any summing-up of effects. A foundation was thus laid in my
thoughts for the principal chapters of what I afterwards published on
the Logic of the Moral Sciences; and my new position in respect to my
old political creed, now became perfectly definite.

If I am asked, what system of political philosophy I substituted for
that which, as a philosophy, I had abandoned, I answer, No system: only
a conviction that the true system was something much more complex and
many-sided than I had previously had any idea of, and that i