There is much difference between the two versions of this episode.
In YBL, the introductory portion is long and full, the actual fight
very short, while in LL the fight is long-drawn-out, and much more
stress is laid on the pathetic aspect of the situation. Hence it is
generally assumed that LL preserves an old version of the episode,
and that the scribe of the Yellow Book has compressed the latter
part. It is not, however, usual, in primitive story-telling, to
linger over scenes of pathos. Such lingering is, like the painted
tears of late Italian masters, invariably a sign of decadence. It
is one of the marks of romance, which recognises tragedy only when
it is voluble, and prodigal of lamentation. The older version of
the _Tain_ is throughout singularly free from pathos of the feebler
sort; the humorous side is always uppermost, and the tragic
suggestions interwoven with it.
But it is still a matter of question whether the whole Fer Diad
episode may not be late. Professor Zimmer thinks it is; but even
the greatest scholar, with a theory to prove, is not quite free. It
will of course be noticed, on this side, that the chief motives of
the Fer Diad episode all appear previously in other episodes (e.g.
the fights with Ferbaeth and with Loch). Further, the account even
in YBL is not marked by old linguistic forms as are other parts of
the tale, while much of it is in the bombastic descriptive style of
LL. In the condition in which we have the tale, however, this
adventure is treated as the climax of the story. Its motive is to
remove Cuchulainn from the field, in order to give the rest of
Ulster a chance. But in the account of the final great fight in
YBL, Cuchulainn's absence is said to be due to his having been
wounded in a combat against odds (_crechtnugud i n-ecomlund_).
Considering, therefore, that even in YBL the Fer Diad episode is
late in language, it seems possible that it may have replaced some
earlier account in which Cuchulainn was so severely wounded that he
was obliged to retire from the field.