Meeussen's rule is a special case of tone reduction in Bantu languages. The tonal alternation it describes is the lowering, in some contexts, of the last tone of a pattern of two adjacent High tones (HH), resulting in the pattern HL. The phenomenon is named after its first observer, the Belgian Bantu specialist A. E. Meeussen (1912–1978). In phonological terms, the phenomenon can be seen as a special case of the Obligatory Contour Principle.