Ga is a tone language, usually described as having high and low tones with downstep (tone terracing). Paster (2003) shows that tone carries grammar in Ga: floating tones mark tense, aspect and mood, the perfective being marked by a floating low tone that can surface as a downstep. Earlier tone rules were proposed by Kropp Dakubu and Trutenau.
In Ga, tone alone can distinguish one verb form from another.