d to a few clearly defined cases.
(1) The author of the document in which the fact is not mentioned had
the intention of systematically recording all the facts of the same
class, and must have been acquainted with all of them. (Tacitus sought
to enumerate the peoples of Germany; the _Notitia dignitatum_ mentioned
all the provinces of the Empire; the absence from these lists of a
people or a province proves that it did not then exist.) (2) The fact,
if it was such, must have affected the author's imagination so forcibly
as necessarily to enter into his conceptions. (If there had been regular
assemblies of the Frankish people, Gregory of Tours could not have
conceived and described the life of the Frankish kings without
mentioning them.)

III. The positive mode of reasoning begins with a fact established by
the documents, and infers some other fact which the documents do not
mention. It is an application of the fundamental principle of history,
the _analogy_ between present and past humanity. In the present we
observe that the facts of humanity are connected together. Given one
fact, another fact accompanies it, either because the first is the cause
of the second, or because the second is the cause of the first, or
because both are effects of a common cause. We assume that in the past
similar facts were connected in a similar manner, and this assumption is
corroborated by the direct study of the past in the documents. From a
given fact, therefore, which we find in the past, we may infer the
existence of the other facts which were connected with it.

This reasoning applies to facts of all kinds, usages, transformations,
individual incidents. We may begin with any known fact and endeavour to
infer unknown facts from it. Now the facts of humanity, having a common
centre, man, are all connected together, not merely facts of the same
class, but facts belonging to the most widely different classes. There
are connections, not merely between the different facts relating to art,
to religion, to manners, to politics, but between the facts of religion
on the one hand and the facts of art, of politics, and of manners on the
other; thus from a fact of one species we may infer facts of all the
other species.

To examine those connections between facts on which reasonings may be
founded would mean tabulating all the known relations between the facts
of humanity, that is, giving a full account of all the empirical laws of
social lif