[i-adj 〜い → 〜さ] + そう Exceptions: ない → なさそう / いい → よさそう
[na-adj] + そう
[v1 stem] + そう [v5 stem] + そう [する → し] + そう / [来る → き] + そう
Negative: [i-adj 〜い → 〜くな] + さそう [na-adj] + ではなさそう / じゃなさそう [v1 stem / v5 stem] + そうにない / そうもない
Modification: ~そうな + [noun] (na-adj behavior) ~そうに + [verb] (adverbial)
~そう is used to express that something looks like or seems like a certain way based on its appearance. It is a subjective judgment based on what the speaker sees or feels.
It expresses conjectures about the present state or a future event. However, it cannot be used to express a conjecture about the past.
Grammatically, そう is a na-adjective: