Scientific discourse has relatively few lexical gaps,
many-to-one or one-to-many lexical correspondences;
informal conversation has relatively many
Lexical gaps
SL content lexical items which don't correspond to TL lexical
items but which must be translated
Translate with the nearest lexical item
Translate as a phrase (though a definition usually isn't
appropriate)
Leave untranslated
SL lexical items or grammatical morphemes which can remain
untranslated (or are normally conveyed by non-lexical
means in the TL)
A statistical approach (IBM)
Given a TL sentence T, find a SL sentence S such that
P(S|T) is maximized.
P(S)
P(T|S): P(WT|WS), "fertility" probabilities
(probability that a word is realized as some number of
words), distortion probabilities: P(i|j,l) (probability
that target position i in sentence of length l
corresponds to source position j)