How does the principle of least effort work in sound change and

How does the principle of least effort work in sound change and grammatical change?
【正确答案】：For sound change, one key motivator is ease of articulation. There is a tendency for intervocalic voiceless plosives to be subjected to lenition because producing a voiced fricative between vowels requires less physiological change than does the production of a voiceless plosive.
For grammatical change, it is not difficult to see that the principle of least effort works for widespread simplification of the grammatical categories in the English language, exemplified by substantial losses of gender, case and tense distinctions.