What are Modal Verbs?
Modal verbs are special verbs which behave very differently from normal verbs. Here are some important differences:
1. Modal verbs do not take "-s" in the third person.
Examples:
- He can speak Chinese.
- She should be here by 9:00.
2. You use "not" to make modal verbs negative, even in Simple Present and Simple Past.
Examples:
- He should not be late.
- They might not come to the party.
3. Many modal verbs cannot be used in the past tenses or the future tenses.
Examples:
- He will can go with us. Not Correct
- She musted study very hard. Not Correct
Common Modal Verbs
Can
Could
May
Might
Must Ought to
Shall
Should
Will
Would
For the purposes of this tutorial, we have included some expressions which are not modal verbs including
had better,
have to, and
have got to. These expressions are closely related to modals in meaning and are often interchanged with them.
Modal Verbs of Probability The Modal Verbs in English
The nine modals verbs in English are:
- can
- could
- may
- might
- must
- shall
- should
- will
- would
Position of Modal Verbs
Modal verbs always appear in the first position at the beginning of the verb phrase in English. Unlike other verbs, modal verbs do not show tense or number. The seven possible verb phrase combinations that contain modal verbs in English are:
- modal verb + base form = will eat
- modal verb + be + present participle = will be eating
- modal verb + have + past participle = will have eaten
- modal verb + be + past participle = will be eaten
- modal verb + have + been + present participle = will have been eating
- modal verb + have + been + past participle = will have been eaten
- modal verb + have + been + being + past participle = will have been being eaten
Double Modals
Although most varieties of English only allow for the use of one modal verb per verb phrase, some English dialects such as Southern American English allow for double modals. For example, the double modal
might could as in
He might could build a new machine shed expresses both possibility and ability. However, prescriptive grammars proscribe against the use of double modals.
Some Definitions of English Modal Verbs
Modal verbs are difficult to define in any language because of the wide range of pragmatic uses of modal verbs by native speakers. Some of the more common definitions (in no particular order) of the modal verbs in English are:
- can – ability, permission, possibility, request
- could – ability, permission, possibility, request, suggestion
- may – permission, probability, request
- might – possibility, probability, suggestion
- must – deduction, necessity, obligation, prohibition
- shall – decision, future, offer, question, suggestion
- should – advice, necessity, prediction, recommendation
- will – decision, future, intention, offer, prediction, promise, suggestion
- would – conditional, habit, invitation, permission, preference, request, question, suggestion
Examples of Modal Verb Usage
The following sentences are examples of usage of modal verbs in English. For example, the following four sentences all ask for permission but with different degrees and types of modality:
- Can I go to the bathroom? (asking for permission)
- May I go to the bathroom? (more politely asking for permission)
- Could I go to the bathroom? (asking for permission with less certainty)
- Might I go to the bathroom? (asking for permission with uncertainty)
The following sentences also demonstrate the subtle meanings in regards to modal verbs of suggestion:
- You could listen to me. (suggestion)
- You might listen to me. (uncertain suggestion)
- You should listen to me. (strong suggestion)
- You must listen to me. (stronger suggestion)
- You will listen to me. (strongest suggestion)
The meanings of modal verbs are very pragmatic and must be learned through use.
Read more:
http://www.brighthub.com/education/languages/articles/37641.aspx#ixzz0TFhcG3AL 
Modals 
Linear Mode
