～そうだ

Rule~sou da has two uses: stem/root + sou (appearance: "looks like / about to") and plain form + sou da (hearsay: "I hear that").

Curiosity

"It looks like it will rain (from what I see)" differs from "I hear it will rain (from someone)." Both use sou da — how do you tell them apart?

Intuition

The connection form splits the two. Appearance (a visual impression) attaches sou directly to the stem/root (furi-sou, taka-sou). Hearsay (something heard) attaches sou da to the plain form (furu sou da, takai sou da). "Direct attachment = looks; plain form = heard."

Visualization

furu (fall) → furi (masu-stem) → furi sou da (looks like it will fall, appearance). For hearsay: furu + sou da = furu sou da (I hear it will rain).

降るdictionary (fall)

Essence

Appearance: verb masu-stem / adjective root + sou (furi-sou, taka-sou, genki-sou; exceptions ii→yosa-sou, nai→nasa-sou). Hearsay: plain form + sou da (furu sou da, takai sou da, gakusei da sou da). Appearance conjugates (furi-sou na sora); hearsay does not.

Examples

空が暗くて、雨が降りそうです。

The sky is dark; it looks like it will rain.

このケーキ、おいしそうですね。

This cake looks delicious.

天気予報によると、明日は雨だそうです。

According to the forecast, I hear it will rain tomorrow.

Mini-quiz

Which fits the appearance "(it looks like) it will fall soon"? (ochiru)