Why is POS specified in the dictionary?

[Anonymous Student]

The lexicon entries have information about the POS of each listed word. But, if I understood correctly, the POS tagging module is used before the pronunciation module which includes the lexicon. Then, why would we need POS in the lexicon? (or a POS tagging module)?

[Simon]

POS is needed in the lexicon to disambiguate homographs. Because POS is the only way to choose the correct pronunciation for words such as “present”, we need to run a POS tagger before trying to look the word up in the lexicon.

In Festival, the lex.lookup_all function will retrieve all matching words and show you their POS tags, for example (for a voice based on the CMU lexicon):

festival> (voice_cmu_us_slt_arctic_hts)
cmu_us_slt_arctic_hts
festival> (lex.lookup_all 'present)
(("present" n (((p r eh z) 1) ((ax n t) 0)))
 ("present" v (((p r iy z) 0) ((eh n t) 1))))

Later in the processing pipeline, the POS tags will also be used to predict phrase breaks.

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