“Shall, should, and must” modal verbs are used to express obligations in the conversations, contracts, or in the public life. Obligation indicates binding agreement or duties on someone to do something. So, different modal verbs are used to express different obligations. Let’s see the correct use and difference among modal verbs for obligation.
Types of obligations
•Forceful obligation — must,
•Legal obligation — shall,
•General obligation — should.
These three modal verbs are commonly used to express obligations according to the prevailing situations.
Must — forceful obligation
“Must” modal auxiliary is perfectly used to express obligations especially in the public places in the interest of public.
•People must not spit in public offices.
•Students must refrain themselves from ragging activities in the college campus.
•People must cooperate to keep clean the natural reservoirs of water.
•Citizens must fulfill theirs national duties in need.
Shall for legal obligation
“Shall” modal auxiliary is preferred to express legal obligation in the agreements, contracts, or legal notices.
•The purchase and sell of plastic bags shall be banned after the commencement of newly passed law.
•The company shall be liable to pay $200 compensation for faulty product.
•The organization shall pay the fine imposed by green tribunal for environmental damage.
Should for polite obligation
“Should” modal auxiliary is perfectly used to express polite obligation in the conversations.
•Everyone should respect national flag.
•Pilgrims should not forget the check out time.
•Students should show teachers daily assignments.
•Citizens should serve for national unity and integrity.
•Everyone should take life skill education.
•Why should I carry extra liabilities ?
•Why should I pay the all bills ?
Modal auxiliary for offers
“Can” modal auxiliary is perfectly used to express offer than “may and shall”.
•Can I help you to complete your assignment?
•Can I do something to solve your problem ?
“May” modal auxiliary is more polite than “can” in respect to make offers.
In this way, by using “shall, should, and must” modal verbs, we can express different types of obligations as per the situations.