oposition; (2) a detailed knowledge of a past fact. It is bad
workmanship to assume a false general proposition--to suppose, for
example, as Augustin Thierry did, that every aristocracy had its origin
in a conquest. It is bad workmanship, again, to found an argument on an
isolated detail (the name of a city). The nature of these errors
indicates the precautions to be taken.

(1) The spontaneous tendency is to take as a basis of reasoning those
"common-sense truths" which form nearly the whole of our knowledge of
social life. Now, the greater part of these are to some extent false,
for the science of social life is still imperfect. And the chief danger
in them lies in the circumstance that we use them unconsciously. The
safest precaution will be always to formulate the supposed law on which
we propose to base an argument. In every instance where such and such a
fact occurs, it is certain that such and such another fact occurs also.
If this proposition is obviously false, we shall at once see it to be
so; if it is too general, we shall inquire what new conditions may be
introduced to make it accurate.

(2) A second spontaneous impulse leads us to draw consequences from
isolated facts, even of the slightest kind (or rather, the idea of each
fact awakens in us, by association, the idea of other facts). This is
the natural procedure in the history of literature. Each circumstance in
the life of an author supplies material for reasoning; we construct by
conjecture all the influences which could have acted upon him, and we
assume that they did act upon him. All the branches of history which
study a single species of facts, isolated from every other species
(language, arts, private law, religion), are exposed to the same danger,
because they deal with fragments of human life, not with comprehensive
collections of phenomena. But few conclusions are firmly established
except those which rest on a comprehensive body of data. We do not make
a diagnosis from a single symptom, but from a number of concurrent
symptoms. The precaution to be taken will be to avoid working with an
isolated detail or an abstract fact. We must have before our minds
actual men, as affected by the principal conditions under which they
lived.

We must be prepared to realise but rarely the conditions of a certain
inference; we are too little acquainted with the laws of social life,
and too seldom know the precise details of an historical fact. Thus most
of