Arva per annos mutant_, we do not
know beforehand whether he took the right method to inform himself, nor
even in what sense he used the words _arva_ and _mutant_; to ascertain
this a preliminary operation is required.[129] This operation is
internal criticism.

The object of criticism is to discover what in a document may be
accepted as true. Now the document is only the final result of a long
series of operations, on the details of which the author gives us no
information. He had to observe or collect facts, to frame sentences, to
write down words; and these operations, which are perfectly distinct one
from another, may not all have been performed with the same accuracy. It
is therefore necessary to _analyse_ the product of the author's labour
in order to distinguish which operations have been incorrectly
performed, and reject their _results_. _Analysis_ is thus necessary to
criticism; all criticism begins with analysis.

In order to be logically complete, the analysis ought to reconstruct
_all_ the operations which the author must have performed, and to
examine them _one by one_, to see whether each has been performed
correctly. It would be necessary to pass in review all the successive
acts by which the document was produced, from the moment when the author
observed the fact which is its subject up to the movements of his hand
by which he traced the letters of the document; or, rather, it would be
necessary to proceed in the opposite direction, step by step, from the
movements of the hand back to the observation. This method would be so
long and so tedious that no one would ever have the time or the patience
to apply it.

Internal criticism is not, like external criticism, an instrument used
for the mere pleasure of using it;[130] it yields no immediate
satisfaction, because it does not definitively solve any problem. It is
only applied because it is necessary, and its use is restricted to a
bare minimum. The most exacting historian is satisfied with an abridged
method which concentrates all the operations into two groups: (1) the
analysis of the contents of the document, and the positive
interpretative criticism which is necessary for ascertaining what the
author meant; (2) the analysis of the conditions under which the
document was produced, and its negative criticism, necessary for the
verification of the author's statements. This twofold division of the
labour of criticism is, moreover, only employed by a sel