Phoneme pair (diphoneme) list

In principle, the length of the diphoneme list is the square of the length of the phoneme list, because the diphoneme list contains every phoneme cooccurring with every phoneme, including itself.

However, there are restrictions and extensions to this:

1. Restrictions: the phonotactics (syllable, phonological word structure) of a language may not permit every combination.
2. Extension (1): internal (diphonemes in the same syllable or simple phonological word) vs. external diphonemes (diphonemes containing a syllable, morpheme or word boundary)
3. Extension (2): prosodically unmarked vs. prosodically marked diphone components (e.g. stress in many European languages, tone in many African and Asian languages)..