tical
interpretation, based on the general rules of the language, must be
supplemented by an historical interpretation founded on an examination
of the particular case.

The method consists in determining the special meaning of the words in
the document; it rests on a few very simple principles.

(1) Language changes by continuous evolution. Each epoch has a language
of its own, which must be treated as a separate system of signs. In
order to understand a document we must know the _language of the
time_--that is, the meanings of words and forms of expression in use at
the time when the text was written. The meaning of a word is to be
determined by bringing together the passages where it is employed: it
will generally be found that in one or other of these the remainder of
the sentence leaves no doubt as to the meaning of the word in
question.[135] Information of this kind is given in historical
dictionaries, such as the _Thesaurus Linguae Latinae_; or the glossaries
of Du Cange. In these compilations the article devoted to each word is a
collection of the passages in which the word occurs, accompanied by
indications of authorship which fix the epoch.

When the author wrote in a dead language which he had learnt out of
books--this is the case with the Latin texts of the earlier middle
ages--we must be on our guard against words used in an arbitrary sense,
or selected for the sake of elegance: for example, _consul_ (count,
earl), _capite census_ (censitary), _agellus_ (grand domain).

(2) Linguistic usage may vary from one region to another; we have, then,
to know the _language of the country_ where the document was
written--that is, the peculiar meanings current in the country.

(3) Each author has his own manner of writing; we have, then, to study
the _language of the author_, the peculiar senses in which he used
words.[136] This purpose is served by lexicons to a single author, as
Meusel's _Lexicon Caesarianum_, in which are brought together all the
passages in which the author used each word.

(4) An expression changes its meaning according to the passage in which
it occurs; we must therefore interpret each word and sentence not as if
it stood isolated, but with an eye to the general sense of the context.
This is the _rule of context_,[137] a fundamental rule of
interpretation. Its meaning is that, before making use of a phrase taken
from a text, we must have read the text in its entirety; it prohibits
the stuf