推量・伝聞N4
〜そうだ
looks like... / I heard that...
Structure
様態：V-ます形（語幹）/ い形容詞（語幹）/ な形容詞（語幹）+ そうだ；伝聞：文（普通形） + そうだ
Explanation
Two uses: ① 様態 (appearance): attaches to the masu-stem of verbs or adjective stems, indicating a direct judgment based on appearance, "looks like..."; ② 伝聞 (hearsay): attaches to plain sentences (dropping だ), indicating reported information, "I heard that...". In the appearance use, ない becomes なさそうだ and いい becomes よさそうだ.
Examples
このケーキはおいしそうです。
This cake looks delicious.
天気予報によると、明日は雨が降るそうです。
According to the weather forecast, it will rain tomorrow.
Note
The two uses conjugate differently: 様態 attaches to masu-stems/stems, 伝聞 to plain sentences. Hearsay cannot be used for things you directly experienced.