Downstep is a phenomenon in tone languages in which if two syllables have the same tone (for example, both with a high tone or both with a low tone), the second syllable is lower in pitch than the first.
Two main kinds of downstep can be distinguished. The first, more usually called automatic downstep, downdrift or catathesis, occurs when high and low tones come in the sequence H L (L) H; the second high tone tends to be lower than the first because of the intervening low toned syllable. That phenomenon is common in African languages, such as Chichewa.  It has also been argued that the same phenomenon causes English sentences, such as I really believe Ebenezer was a dealer in magnesium or I bought blueberries, bayberries, raspberries, mulberries, and brambleberries (if the sentences are pronounced with a falling intonation), to fall gradually in pitch, with each accented syllable (here underlined) slightly lower than the last.
Downstep proper, or non-automatic downstep, is another phenomenon found in many African languages such as Igbo. (See Downing & Rialland 2017 for an overview of downstep in African languages.) If two high tones are in succeeding syllables (thus in the sequence H H), the second is lower than the first. In such languages, when two high tones come one after the other, they are at the same height or, if there is a downstep, the second one is lower. The second high tone is also lower than the preceding one if there is an intervening low tone in the sequence H L H as described above. The high tones in a simple sentence tend to descend from the beginning to the end of the sentence in a series of steps, a phenomenon that Is known as tone terracing.
The symbol for the second kind of downstep in the International Phonetic Alphabet is a superscript down arrow, ⟨ꜜ⟩. It is common to see instead a superscript exclamation mark ⟨ꜝ⟩ because of typographic constraints.
It has been shown that in most, if not all, cases of downstep proper, the lowering of the second high tone is from an intervening low-toned syllable that has dropped out. What was H L H has become H H. The missing low-toned syllable creates what is known as a 'floating tone'. An example occurs in Bambara, a language spoken in Mali. Its definite article is a floating low tone. With a noun in isolation, it docks to the preceding vowel and turns a high tone into a falling tone:
However, when it occurs between two high tones, it downsteps the following tone:
|/bá tɛ́/||it's not a river|
|/bá ꜜ tɛ́/||it's not the river|
- Yip (2002), p.148.
- Beckman & Pierrehumbert (1986), p.272.
- Myers (1996).
- Pierrehumbert (1980), pp.139ff, 329ff; Beckman & Pierrehumbert (1986), p.273.
- Connell (2001)
- Downing/Rialland, Laura J./Annie (2017). Intonation in African tone languages. Berlin: De Gruyter. ISBN 3110503522. OCLC 963605080.
- Welmers (1974), pp.82ff
- Welmers (1974), p.87.
- Beckman Mary E. & Janet B. Pierrehumbert, (1986). "Intonational Structure in English and Japanese". Phonology Yearbook 3, 255-309.
- Connell, Bruce (2001) "Downdrift, Downstep, and Declination". Typology of African Prosodic Systems Workshop, Bielefeld University, Germany
- Crystal, David (2003). A dictionary of linguistics & phonetics. Wiley-Blackwell, pg. 130.
- Myers, Scott (1996). "Boundary tones and the phonetic implementation of tone in Chichewa", Studies in African Linguistics 25, 29-60.
- Pierrehumbert, Janet B. (1980) "The Phonology and Phonetics of English Intonation" Ph.D. Thesis, Massachusetts Institute of Technology.
- Welmers, William E. (1974). African Language Structures. University of California Press.
- Yip, Moira (2002). Tone. Cambridge University Press.