Modal Verbs: Ability. Advice, Necessity and Obligation. Possibility and Certainty.

Hi, everyone! We're going to revise the form and use of modal verbs.

Form.

The first thing we have to know is the type of modal verbs there are:

Pure modals	Semi-modals
can	be able to
could
may	have better
might
must	have to
shall
should
ought to
will
would
need ***	need to

*** need is a special verb since as a modal it is almost always negative such as you needn't come to work tomorrow
The pure modals are used just exactly as the auxiliary verbs in the sentence word order.

Subject	Modal / Auxiliary	Verb	Object	Manner, place and time
You	shouldn't	be	so stressed	for driving
You	needn't	drive		to school
I	can	give	you	a lift

Their main difference is that pure modals are invariable forms, that is, we can't use them in the past or future forms.
Instead, the semi-modals can be used in the past, future and the rest of tenses too.

Use.

For understanding the meaning and use of the modal verbs we can establish different uses: ability; advice, necessity, and obligation; possibility and certainty.

Ability

We express ability by means of the modals can and could and the semi-modal be able to.
Here a presentation to learn more about the modals of ability:

Modals - Ability from thelecturette.com

Exercises:

• http://www.perfect-english-grammar.com/modal-verbs-of-ability-exercise-1.html
  
• http://usefulenglish.ru/grammar/modal-verbs-exercise-one
  
• http://www.learnenglish-online.com/grammar/modals/tests/modalability.html
  

Advice, necessity, and obligation

For expressing advice we have the modals:

• should and ought to (ought to isn't usually used in the negative and interrogative form) to express advice.
  
• need to to express necessity (only in the affirmative form).
  
• needn't (without to) and the don't/doesn't have to are used to make clear there's no need to do something.
  
• must and have to express obligation.
  
• mustn't for expressing prohibition (obligation of not doing)
  

For more information, you can watch these presentations

• Advice
  

Advice, should, shouldn't, ought to, had better, and had better not from Online English Courses

Exercises:

http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/330-modals-advice1.htm

• Necessity
  

Modals of necessity from UTPL UTPL

Exercises:

http://usefulenglish.ru/grammar/modal-verbs-exercise-three

• Obligation
  

Modals for obligation and prohibition from David Mainwood

Exercises.

http://www.autoenglish.org/modalverbs/ModalsObligation.htm

Possibility and certainty

The modal verbs we use to express possibility and certainty are may, might, can, could, must

• to express possibility in the present or the future we may (may not), might (mightn't) and could.
  
• To express logical deduction we use must (in the affirmative form) or can't (in the negative form).
  
• When we are sure something is true we use must.
  
• When we are sure something is impossible we use can't.
  

Modals of Possibility and Certainty from David Mainwood

Exercises:

http://speakspeak.com/english-grammar-exercises/intermediate/intermediate-grammar-exercise-modal-verbs-for-present-probability-must-cant-could-may-might