obligation / need / possibility
obligation : 義務
- [形]liable : 法的な義務の意味も含む
You will be liable for any damage when you rent a car
The company is obliged to give a refund if the tour is cancelled
- [形]forced : 強制（make的な使い方）
The bank robbers forced him at gunpoint to open the safe.
- have no choice/alternative but : するしかない
We had no choice/alternative but to sell our house.
- [形]mandatory : 必須の(法律、ルール、約束などによって強制される性質のもの,免れないみたいな？)
The death sentence is mandatory for drug-smuggling in some countries.
- [形]compulsory / obligatory : 強制
Was sport compulsory/obligatory at your school?
Need : 必要
- in need of : ~を必要として(needs/wantsよりフォーマルな言い方)
This plant is in need of water.
- need for : 〜を必要とする (we feel a need)
There’s need for more discussion on the matter.
- an absolute necessity : 必ず必要
A car is an absolute necessity if you live in the countryside and there is no public transport.
- requirements : 必要条件
What are the requirements for a Master’s course in English?
possibilities : 可能性
- Is there any chance/possibility you’ll be free next week?
- [形]inevitable : 必然
A rise in oil prices is inevitable as oil supplies run out across the world.
- It is doubtful whether : かどうかは怪しい
It is doubtful whether the economy will improve next year.
- It is probable that : たぶん〜だろう
It is probable that the next government will change the tax laws.
- certainty : 確実
Most scientists believe that climate change is no longer just a possibility but is now an absolute certainty.