that's why; no wonder; it follows that

わけだ presents a conclusion that follows logically from the situation, often as a realization. Attach it to a plain-form verb/adjective, a noun with の/という, or a na-adjective with な. It says given all that, naturally this is the case.

Examples

• 三さん年ねんも住すんでいたのか。日本語にほんごが上手じょうずなわけだ。

  San nen mo sunde ita no ka. Nihongo ga jouzu na wake da.

  You lived there three years? No wonder your Japanese is good.

• 今日きょうは祝日しゅくじつだから、銀行ぎんこうが休やすみなわけだ。

  Kyou wa shukujitsu da kara, ginkou ga yasumi na wake da.

  It's a holiday today, so that's why the bank is closed.

Vocabulary in these examples

• 三 three
• 年 year; age
• 住む to live; to reside
• いる to exist (animate); to be
• 日本語 Japanese language
• 上手 good at; skillful

Related patterns · Nominalizers and explanation

• 〜はずだ should be; is supposed to be (expectation)
• 〜べきだ should; ought to (strong advice)
• 〜ということだ I hear that; it means that