by the
weakness of oral tradition. In the former case, we have to ask what was
the trustworthiness of the original records, and how far do the extant
writings fairly represent those records?

Our answers to these questions will partly depend upon what we know or
can discover of the authors of the MSS. or books. Who was the author? If
a work bears some man's name, did he really write it? The evidence
bearing upon this question is usually divided into internal, external
and mixed; but perhaps no evidence is purely internal, if we define it
as that which is derived entirely from the work itself. Under the name
of internal evidence it is usual to put the language, the style,
consistency of ideas; but if we had no grounds of judgment but the book
itself, we could not possibly say whether the style was the author's:
this requires us to know his other works. Nor could we say whether the
language was that of his age, unless we knew other literature of the
same age; nor even that different passages seem to be written in the
manner of different ages, but for our knowledge of change in other
literatures. There must in every case be some external reference. Thus
we judge that a work is not by the alleged author, nor contemporary with
him, if words are used that only became current at a later date, or are
used in a sense that they only later acquired, or if later writers are
imitated, or if events are mentioned that happened later
('anachronism'). Books are sometimes forged outright, that is, are
written by one man and deliberately fathered upon another; but sometimes
books come to be ascribed to a well-known name, which were written by
some one else without fraudulent intent, dramatically or as a
rhetorical exercise.

As to external evidence, if from other sources we have some knowledge of
the facts described in a given book, and if it presents no serious
discrepancies with those facts, this is some confirmation of a claim to
contemporaneity. But the chief source of external evidence is other
literature, where we may find the book in question referred to or
quoted. Such other literature may be by another author, as when
Aristotle refers to a dialogue of Plato's, or Shakespeare quotes
Marlowe; or may be other work of the author himself, as when Aristotle
in the _Ethics_ refers to his own _Physics_, or Chaucer in _The
Canterbury Tales_ mentions as his own _The Legend of Good Women_, and in
_The Legend_ gives a list of other works