Haspelmath, Sims. Understanding Morphology (2010 2 ed). p 214 Bottom - 215 Top.
Automatic alternations are the [1.] synchronic [End of 1.] consequence of phonetically-motivated diachronic sound changes. Sound change is motivated by phonetics in the sense that it occurs because phonetic production is made
easier by the change. For example, pronouncing an alveolar or velar consonant before [i] is relatively more difficult than pronouncing a palatal (or palatalized) consonant, and this explains why the diachronic change of palatalization before front vowels is so common in the world’s languages (e.g. (10.1d)). Final devoicing helps pronunciation because maintaining the vibration of the vocal chords (which is made difficult by the oral obstruction of obstruents anyway) is particularly difficult in the final position (e.g. (10.1a)). Neutralization of unstressed vowels occurs for perceptual reasons: when a vowel is not stressed, it is less loud and thus differences between vowels are harder to perceive (e.g. (10.1c)). As in German Umlaut, morphophonological alternations often result when the phonetic motivation for some automatic alternation is subsequently obscured.
[p 326:] diachronic: having to do with language change over time (Section 6.1) (cf. synchronic).
[p 343:] synchronic: having to do with language at
a given point in time(Section 6.1) (cf. diachronic).
I don't understand 1. Oughtn't 'synchronic' be 'diachronic'?
'a given point in time` means a short time period like a day. Am I correct? If not, what time period did the authors envisage?
Even if the authors intended 'a given point in time' to mean a year or decade, how can automatic alternations be synchronic? One year or decade isn't long enough to spur phonological changes.