～だろう

だろう is the plain form of でしょう: a guess, "probably", "I suppose". It follows the plain form of a verb or an い-adjective, and comes straight after a noun or a な-adjective, with no だ in between.

• × 学生だだろう → 学生だろう
• × 簡単なだろう → 簡単だろう
• × 行きますだろう → 行くだろう

For a guess about the past, put the plain past in front: いった行っただろう, たかかった高かっただろう, がくせい学生だっただろう.

だろう or でしょう

The two mean the same; they differ in register. でしょう is polite and works anywhere. だろう is the normal form in essays, news writing and thoughts; in conversation it sounds blunt and masculine, and でしょ is the softer casual form.

Usage notes

These go beyond a plain guess.

Checking with the listener

With a rising intonation, だろう？ asks the listener to agree: "right?", "isn't it?". The speaker is fairly sure already.

だろうと思う

In speech a guess often ends in とおもう思う, which makes it personal and softer. The polite form is だろうと思います.