Should be with 〜べきだ
Adding べき to the end of a sentence gives the meaning that the speaker believes someone should do something, or something should be in some state.
When used as an auxiliary, べき is followed by だ. Changes in tense and negation are done to this だ.
If べき preceeds a noun, だ is omitted.
- 〜べきだ｜日本語能力試験 JLPT N２ (www.edewakaru.com)
