translation shifts

As far as translation is concerned, Catford makes an important distinction
between formal correspondence and textual equivalence, which was later to
be developed by Koller (see chapter 3):
A formal correspondent is 'any TL category (unit, class, element of
structure, etc.) which can be said to occupy, as nearly as ~ossible,t he
"same" place in the "economy" of the TL as the given SL category occupies
in the SL' (Catford 1965: 27).
A textual equivalent is 'any TL text or portion of text which is observed
on a particular occasion . . . to be the equivalent of a given SL text or
portion of text'.
Textual equivalence is thus tied to a particular ST-TT pair, while formal
equivalence is a more general system-based concept between a pair of languages.
When the two concepts diverge, a translation shift is deemed to have
occurred. In Catford's own words (2000: 141), translation shifts are thus
'departures from formal correspondence in the process of going from the SL
to the TL'.