A floating tone is a morpheme or element of a morpheme that contains no consonants, no vowels, but only tone. It cannot be pronounced by itself, but affects the tones of neighboring morphemes.
An example occurs in Bambara. Bambara has two phonemic tones,high and low. In this language, the definite article is a floating low tone. With a noun in isolation, it is associated with the preceding vowel, turning a high tone into a falling tone: [bá] river; [bâ] the river. When it occurs between two high tones, it downsteps the following tone:
[bá tɛ́]it's not a river
[bá tɛ̄] (or [bá ꜜ tɛ́]) it's not the river
Also common are floating tones associated with a segmental morpheme such as an affix. For example, in Okphela, an Edoid language of Nigeria, the main negative morpheme is distinguished from the present tense morpheme by tone; the present tense morpheme (á-) carries high tone, whereas the negative past morpheme (´a-) imposes a high tone on the syllable which precedes it:
oh á-nga he is climbing
óh a-nga he didn't climb
Floating tones derive historically from morphemes which assimilate or lenite to the point where only their tone remains.
^Clark, Mary M. 1993. "Representation of downstep in Dschang Bamileke". The PhOilOlogy of Tone: The Representation of Tonal Register, ed. by Harry van der Hulst and Keith Snider. Berlin/New York: Mouton de Gruyter. Pp. 29-73
^Wentum, Comfort. 1997. A Lexical Tonology of Ga. Legon: University of Ghana, M. Phil thesis.
^Clements, G. N. and Kevin C. Ford. 1979. "Kikuyu tone shift and its synchronic consequences." Linguistic Inquiry 10: 179-210.
^Kropp-Dakubu, Mary E. 1986. "Downglide, floating tones and non-WH questions in Ga and Dangme." The Phonological Representation ofSuprasegmentais, ed. by Koen Bogers, Harry van der Hulst, and Maarten Mous. Dordrecht: Foris Publications. Pp. 153-173.
^Zimmerman, 1. 1858. A grammatical sketch and vocabulary of the Akra- or Galanguage with an appendix on the Adanme dialect. Stuttgart, 2 vols. Republished with an Introduction by 1. Berry, Gregg International, 1972.