 For example, when the possessive suffix "-šu" is added to the root "awat" ('word'), it is written "awassu" ('his word') even though "šš" would be expected.The most straightforward interpretation of this shift from "tš" to "ss" is that /s, ṣ/ form a pair of voiceless alveolar affricates , *š is a voiceless alveolar fricative , and *z is a voiced alveolar affricate or fricative .The assimilation is then [awat+su] > .