We have already met one way to make a suggestion.
| タバコをやめた方がいいです。 |
| It’s better that you quit smoking. |
べき expresses a similar meaning, but is much more forceful—to the point where it is almost an order. While you may hear it in speech it is a considerably hard expression and is more often used in writing.
| タバコをやめるべきです。 |
| You should quit smoking. |
| 約束を守るべきだ。 |
| You should keep promises. |
| 足が痛いなら医者に診てもらうべきだと思います。 |
| If your leg hurts I think you should have the doctor take a look at it. |
When used with the verb する it is usually abbreviated.
するべき → すべき
| 留学すべきかどうかについて、親と真剣に相談します。 |
| Seriously discuss with parents whether or not you should study abroad. |
Unlike はず no particle is required to modify a noun.
| 絶対守るべき約束。 |
| A promise you should definitely keep. |
べき can also be used to express a likely result, as well.
| 驚くべき発見。 |
| Surprising discovery. |
べき can be changed to the negative by conjugating the auxiliary verb.
| 車がなくても赤信号の時に、渡るべきではない。 |
| Even if there aren’t any cars you shouldn’t cross the road when the lights are red. |
| この町の治安が悪いから夜に家を出掛けるべきではない。 |
| This town isn’t safe and so at night you shouldn’t leave the house. |
A more literary way of forming the negative is with べきからず.
| イギリスでは高速道路で時速７０マイル以上運転すべからず。 |
| In England you should not drive at over 70mph on the motorways. |
Incidentally, べし is the archaic form of べき. You may occasionally see it writing, but it is rarely ever used in speech.