Follow these Rules! (Modal Verbs of Obligation)

rule; /ro͞ol/ (n.)
An authoritative statement of conduct.

At home, in school, on the bus, around the airport… the list is endless!

Everywhere we go there are rules to follow. Keep yourself out of trouble with these Modal Verbs of Obligation.

‘have to’/’dont have to’ + infinitive:

(a) “Today is Tuesday and I have to work”.

Here, there is a strong obligation for me to do something. I like my job and I would certainly like to keep it. However, soon it will be Saturday and luckily for me, (b) “I don’t have to work at the weekend”. So, on Saturday there is NO obligation for me to go into EC: I can watch the soccer, buy some groceries or if I’m really tired, just stay in bed! I COULD work if I wanted to, but its the weekend so I think I’ll enjoy some time off.

‘must’/’musn’t’ + infinitive

Now, lets look at the following statements:
(c) “I must visit the doctor, I’m terribly sick”.
(d) “Excuse me, Sir. This is a public building. You mustn’t smoke”

In statement (c), we can see there is a slightly STRONGER obligation for me to do something than in (a). Of course, my job IS important, however, I am more worried about my health.

In statement (d), there is not just a rule, but a legal rule. Here, we are talking about the LAW.

Finally, let’s take a look at ‘should’/’shouldn’t’ + infinitive.

(e) “Julia has been spending too much in Macy’s. She should save her money for something useful”.
(f) “You shouldn’t drink so much Coca-Cola. It is bad for your teeth”.

In both (e) and (f), we can see two examples of what are considered ‘mild’ obligations or advice. Julia does not HAVE to save her money, but she SHOULD. Instead of buying new clothes, she could save-up and do more on her vacation.

In (f), the situation is very similar. The only difference is that we are using the negative ‘shouldn’t’. Coca-Cola is bad for our teeth, but if my friend loves its sweet taste, he probably doesn’t care! This means he will probably ignore my advice.

In summary, now we know:

‘have to’/don’t have to’ + infinitive = strong obligations

‘must’/’musn’t’ + infinitive = stronger obligations AND rules to do with the law.

‘should’/’shouldn’t’ + infinitive = mild obligations AND general advice.

Remember, “He that cannot obey (the rules), cannot command (them)”– Benjamin Franklin