～そうです (様態)

The etymology of '～そうです' for describing appearance or likelihood is rooted in classical Japanese. The 'そう' (sou) part originally comes from '様' (sama), meaning 'appearance' or 'state'. Over time, it evolved into an auxiliary verb particle that attaches to the stem of verbs or i-adjectives, or to the stem of na-adjectives (dropping the 'na'), to indicate that something 'looks like,' 'seems like,' or 'appears to be' in a certain state or about to do something. The 'です' (desu) is the polite copula, making the expression polite. This construction has been a stable part of Japanese grammar for centuries, used to convey observations or inferences based on sensory information rather than direct knowledge.