sibilant alternates with or , depending on the root. The velar alternates with . Both and alternate with , but does not change in a weakening context. The lateral alternates with both [ɮ] and . Sonorants weaken by becoming glottalized. In addition to the somewhat unpredictable set of changes, the patterns involved in weakening are further complicated by the fact that some suffixes weaken stops but do not affect fricatives. Boas lists 11 suffixes weakening stops and affricates but not fricatives; these suffixes are indicated by the notation ⟨=⟩ as seen in the following list: /=/ "continuously"; /=/ "mouth, opening, to talk about"; /=/ "away"; /=/ or /=/ "to do something while doing something else" – weakens ; (=) "continuing motion in a definite direction" – weakens , , ; (=) "to go attend, to be on the way"; /=/ "place where there are many (plants etc.)" – does not weaken ; /=/ "canoe"; /=/ "in front of house, body, mountain"; /=/ "by force"; /=/ "moving on water". Hardening suffixes trigger fortition in most cases. Stem-final plain stops or affricates or sonorants become glottalized. As with weakening suffixes, the hardening patterns of fricatives are less predictable. hardens to or . (The classification is apparently arbitrary and not necessarily consistent with the weakening behavior of a given stem; a stem in which becomes when weakened may become either or when it is hardened, etc.) hardens to . Both and harden to , while in a hardening context surfaces with an additional following glottal stop: . hardens to . The table below illustrates how various roots weaken and harden. Stem expansion In addition to fortition and lengthening, suffixes may also be associated with lengthening or reduplication effects on the stems which precede them. distinguishes seven classes of suffix (with many subclasses), which all have different effects on some of the twenty possible root shapes which he identifies: Key: The chart follows the one given in , with a few alterations. Root shapes refer to an initial consonant C, a nucleus or a full vowel V, and final consonants including plain voiceless obstruents (T), voiced obstruents (D), glides (Y), other sonorants (R) and glottalized versions of each of T and R (Tʼ and Rˀ). Cells show the effect of suffixes belonging to the various classes (columns) on roots or stems of various shapes (rows). = indicates that the suffix leaves the stem unchanged.