Downstep

Downstep is a phenomenon in language where when two syllables have the same tone (for example both have high tone, or both have mid 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; then the second high tone tends to be lower than the first because of the intervening low toned syllable. This phenomenon is common in African languages. It has also been argued that it is this same phenomenon which causes English sentences such as I really believe Ebenezer was a dealer in magnesium or I bought blueberries, bayberries, raspberries, mulberries, and brambleberries (if these 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 on the other hand is a phenomenon found especially in West African languages such as Igbo when of two high tones in succeeding syllables (that is, in the sequence H H) the second is lower than the first. In such languages, when two high tones come one after the other either 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, in the sequence H L H as described above. Thus the high tones in a simple sentence tend to descend downwards from the beginning to the end of the sentence in a series of steps, a phenomenon known as tone terracing.