CD
modals: ability, obligation
(present I future).
ability: can,can't, cannot
Can't is the negative, withcannot as a formai and written form. There is no third person-sform.
Question forms areCan I, Can youetc.
Usecan/can't- to describe ability ar lack of it.
Many animals can see c1early in the dark. Human beings can't do this. - to describe what is allowed ar not allowed.
You can look at the animals in the zoo but you can't touch them. - with a future meaning.
Sorry, but I can't come to the party next week. - with verbs of perception: hear, see, taste, feel, smell.
What can }iou see? I can smell gasi
ability: be able to
This has the same meaning ascan.
Usebe able to- instead ofcan.
Many animals are able tosee in the dark. - whencan is unsuitable. Becausecanhas only present and past forms, we usebe ableto for other
tenses, and infinitive form.
I haven't been able tofinish myproject. Wehope tobe able tovisit you next month.
obligation: have to /hasto
The forms follow have: I have to, he/she has toetc;do I have to, does she have to; I don't haveto etc.
Usehave to/hasto- to describe what is necessary,a rule, or something we do because other people tell
us to.
Baby birds have tolearn how to fly ar they won 't survive.
Do we have tobuy another ticket to see this part of the castle?
The negative form,don't /doesn't have to,is used to describe something unnecessary.
I don'thave to goto work tomorrow. There'saholiday
obligation: must /mustn't
The negative ismustn't, withmust not as a formai and written form. There is no third person-sform.
Question form ismust I, must youetc.
Usemustto describe something we personally think is necessaryand important to do.- There is sometimes little difference between first personI must andI have to.
Sorry, I really have to gonaw. Sorry, I really must gonaw! - In other contexts, there is a difference.
You must be more careful! (=personal opinion of the speaker)
Wehave towear safetygoggles. (= an 'outside' opinion or rule) - We usually use the question form ofhave to formusf.
Do I have tosit here? - We usemustn't when we think an action is against the rules.
You mustn't throw things in the science lab! It's dangerous! - Comparemustn't anddon't have to.
You mustn't useapencil. (it's not allowed)
You don't have touseapen. (it's not necessary- use a pen or a pencil)