ENGLISH MODAL VERBS

On this post we are going to give basic information on ENGLISH MODAL VERBS:
MAIN CHARACTERISTICS:

1-Each verb has its different concept meaning or function. (Look at the chart above)

2- These verbs aren't conjugated. 
No "-S" in the third person singular present.  He can swim. (Not: *He cans swim)
They lack some verb forms, which are covered by semimodals of a similar meaning.
  He had to leave. (Not *He musted leave. Must doesn't have a simple past form)
  He will be able to do it. (Not *He will can do it. Can doesn't have a future form)
[Semi-modal verbs that are used instead of the modal are:
HAVE TO for MUST (obligation)
BE ABLE TO for CAN (ability)
BE ALLOWED TO for CAN, MAY (permission)]

3- They work as auxiliary verbs in the NEGATIVE and QUESTIONS.
  Can I open the window? No, you can't open the window, it's cold.

4-  These verbs are always followed by INFINITIVE WITHOUT TO.
  He can swim. (Not * He can to swim)
Except OUGHT TO.  You ought to go to the doctor's.

5- PERFECT MODALS: past modal verb+HAVE+Past Participle refer to the past.
She hasn't arrived yet. She might have missed the bus.
You failed the exam. You should have studied more.


Link to:
- +INFO & EXERCISES: Perfect English Grammar.
- +INFO @ EXERCISES:English Page.
- +EXERCISES (Modals & their substitutes): Ego4U.

Summary chart: