Additive supralinear morphemes (consisting solely of suprasegmental phonemes) are intonational units and tonal morphemes. Additive morphemes of these last variety are not common [...]
- Nida (1948), Pag. 440

In Kissi, polysyllabic verb stems have no indipendent basic tone, but are accompanied four sets of tone patterns indicating mode-aspect and number-person categories. With plural subject, the typical verb 'baŋa' 'redeem' has the following tones: 'bàŋá' completive, 'bàŋà' incompletive, 'báŋà' negative, and 'bÀŋÀ' interrogative. The tones on the verbs are in no way associated with basic morphological classes of verbs, and hence are genuine additive morphemes.
- Nida (1948), Pag. 440