write + should do
kaku beki da
should do; ought to do
meaning: should write
そう思うなら、本人に直接言うべきだよ。
sou omou nara, honnin ni chokusetsu iu beki da yo.
If you think so, you should say it to her directly. casual
約束は守るべきだ。
yakusoku wa mamoru beki da.
Promises should be kept. neutral