Linguists referring to ‘fast speech’ and to ‘normal speech’ often do not share the same definitions of the two terms. ‘Fast speech’ is normally intended as increase in speech tempo that affects the normal/slow norm, but it is also recognized that ‘fast speech phenomena’ occur in casual speech that is not necessarily rapid, and that ‘casualness’ of speech is a complex sociolinguistic notion the components of which are hard to isolate (see, for instance, Dressler, 1974, and Vanecek et al, 1975, for a discussion of the correlation between decreased attention and phonological casualness, and other factors referred to in Dressler, 1975). It is not at all clear what ‘normal speech’ is either. It is usually identified with ‘maximally distinct/differentiated speech’, but as pointed out to me by Arnold Zwicky, this is probably not the case, since there are processes that apply to give 'careful‘ or ‘;emphatic‘ speech (as when the l in please is made syllabic). Zwicky believes that normal speech ‘is related to whatever level of representation (roughly the phonemic) figures in normal rhyming (hat and had will not count as rhymes, even if they are pronounced the same, while stepped and slept will count as rhymes, even if they are pronounced differently, say without the t in slept)’ (personal communication). This paper does not attempt to tackle the problem in its entirety; it will only deal with the tempo aspect of fast speech and with the theoretical implications of increase in rate of speech. The reason for concentrating on tempo is that it can be isolated more easily than the various factors, social and other, involved in casual speech. It will also be assumed that speech tempo is relative, i.e. that one man's normal rate of speech may be another man's fast speech tempo, and that although increase in speech tempo may sometimes result in increased attention and thus in retention of the overall level of formality (Vanecek et al, 1975), the common tendency is for increased reduction and assimilation with the increase in the rate of articulation.