The document discusses modal verbs and their main features. Modal verbs are followed by the infinitive form of another verb without "to", don't take verb endings, and are never used with other auxiliary verbs. They are used to express ability, obligation, prohibition, certainty, possibility, advice, lack of obligation, and impossibility. The modal perfect tense is used to talk about past alternative actions, past certainties, past possibilities, past impossibilities, and past criticisms.

1. MODAL VERBS
 MAIN FEATURES
MODAL VERBS
MODAL PERFECT

2. MAIN FEATURES
 They are followed directly by the infinitive of another verb (without
TO)
 They don’t use an ‘s’ for the third person singular or ‘ed’ for the
past
 They are never used with other auxiliary verbs. QUESTIONS are
formed by inversion. NEGATIVE is formed adding NOT to the verb

3.  TO TALK ABOUT ABILITY:
MODAL VERBS
CAN/CAN’T
COULD/COULDN’T
BE ABLE TO/ NOT BE ABLE TO
 TO EXPRESS OBLIGATION:HAVE TO/ NEED TO/ NEEDN’T
MUST (not MUSTN’T)
 TO EXPRESS PROHIBITION: MUSTN’T
CAN’T
 TO EXPRESS CERTAINTY THAT SOMETHIG IS TRUEMUST
 TO EXPRESS POSSIBILITY
MAY/ MAY NOT
MIGHT/ MIGHT NOT
COULD/ COULDN’T
 TO GIVE ADVICE
TO MAKE
SHOULD/
SHOULDN’T
OUGHT TO
 TO EXPRESS LACK OF OBLIGATION:DON’T HAVE TO/ NEEDN’T
 TO EXPRESS CERTAINTY THAT SOMETHIG IS IMPOSSIBLECAN’T

4. MODAL PERFECT
 TO EXPRESS AN ALTERNATIVE PAST ACTION:
CAN’T HAVE + PARTICIPLE
 TO EXPRESS A CERTAINTY IN THE PAST:MUST HAVE + PARTICIPLE
 TO EXPRESS A POSSIBILITY IN THE PAST:MAY/ MIGHT HAVE + PARTICIPLE
TO EXPRESS A IMPOSSIBILITY IN THE PAST:
COULD/ WOULD HAVE +
PARTICIPLE
TO SUGGEST A CRITICISM FOR A PAST ACTION:SHOULD HAVE + PARTICIPLE