The evidence for F0 downtrends in Mambila is different across tones, and where downtrends do occur, it is not yet clear whether these are to be attributed to declination or final lowering. Regardless, any downtrends that do occur are slight; Mambila appears to be a discrete-level language, in that any impingement of one tone in the space of another is rapidly corrected. In some respects, therefore, tone realization in Mambila seems relatively straightforward. In particular, we seem not to be faced with the question of how to model the phonetic effect of downstep carrying on through subsequent tones. The reason given for this relatively uncomplicated aspect of Mambila tone is based in the phonology of Mambila: with the register being relatively crowded, having four level tones and several combinations of these at the lexical level, and with these being potentially subject to modification at the grammatical level, there is accordingly less room for maneuver on other planes. There is, in other words, a trade-off between complexity and simplicity at different levels of the linguistic structure; the only phonetic perturbations the phonology permits are sufficiently small that they do not endanger phonological contrast.