A floating tone is a morpheme or element of a morpheme that contains neither consonants nor vowels, but only tone. It cannot be pronounced by itself but affects the tones of neighboring morphemes.
An example occurs in Bambara, a Mande language of Mali that has two phonemic tones,high and low. The definite article is a floating low tone, and with a noun in isolation, it is associated with the preceding vowel and turns a high tone into a falling tone: [bá] river; [bâ] the river. When it occurs between two high tones, it downsteps the following tone:
[bátɛ́]it's not a river
[bátɛ̄] (or [báꜜtɛ́]) 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 that only their tone remains.
^Clark, Mary M. 1993. "Representation of downstep in Dschang Bamileke". The Phonology 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 of Suprasegmentais, 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.