This chapter turns to deletion rules, as well as other kinds of allomorphy, some of which can be recovered only historically. The first set of changes to be considered produces allomorphic variation due to the dropping of one or more phonemes from the edges of the original forms of roots or affixes. Like replacement rules, deletion rules must be defined in terms of both the phonological environment and the type, position, and number of morphemes involved in the change.

Consonant deletion

No double consonants. The general principle which governs the simplification of double consonants to single ones, phonetically, is that English, unlike Italian, Finnish, and many other languages, does not allow “long” or “double” consonants within a word. Our discussion of double consonant spelling in section 4.2, Chapter 6, pointed out the important distinction between double consonants in the spelling, which can arise as a consequence of total assimilation, and “long” consonants in the pronunciation. Word-internal double consonant letters are not pronounced “long”: irrational and eradicate have the same [r], symmetry and cemetery have the same [m].

English allows real long, or geminate, consonants, only at clear morpheme/word boundaries: file log, roommate, bus-schedule, bookcase, letter writer, etc. In such instances longer duration is a phonetic phenomenon only; it is unrelated to spelling. Nevertheless, there is a parallel between real long consonants and the double letters resulting from the total assimilations of Chapter 6: both are signals of morpheme boundaries.