1. Modal verbs do not take suffixes like -s, -ing, or -ed and are followed by the bare infinitive without "to". 2. They come before the subject in questions and are followed by "not" in negations. 3. Modal verbs do not have tenses in the normal sense and are followed by a present or perfect bare infinitive depending on if the action is incomplete or complete.

1. MODAL VERBS
STRUCTURE
1- DO NOT TAKE -S, -ING, OR -ED SUFFIXES
( shouldS shouldED shouldING arenot correct)
2- FOLLOWED BYTHE BARE INFINITIVE( INFINITIVEWITHOUTTO)
( SHOULD TO DO is not correct)
3- COME BEFORETHE SUBJECT INQUESTIONS AND ARE FOLLOWED BYNOTIN
NEGATIONS. Example: MUST I do this? No, you MUSTN’T do it
4- THEY DO NOT HAVETENSES INTHE NORMAL SENSE ( I WILL MUSTis not correct, I am
MUSTING is not correct)
5- THEY ARE FOLLOWED BYA PRESENT BARE INFINITIVEWHENTHEREFER TO AN
INCOMPLETEACTIONORSTATE.
a. We SHOULD STOP the show ( Present)
b. You SHOULD BE STUDYING more ( Presentcontinuous)
6- THEY ARE FOLLOWED BYA PERFECT BARE INFINITIVETO REFERTO A COMPLETE
ACTIONORSTATE.
a. They SHOULD HAVERUN more today
b. They SHOULD HAVEBEEN STUDYING moretoday.
USES ( MODALITY)
OBLIGATION /DUTY / NECESSITY
 MUST expresses DUTYor STRONG OBLIGATION. Ex: I MUSThelp my brother.
 HAVETO expresses STRONG NECESSITY/ OBLIGATION. Ex: I HAVE TO study harder.
 HAD TO is the past formof MUST and HAVE TO. Ex: I HAD TO help my brother to
study maths.
 SHOULD/OUGHTTO express DUTY, WEAK OBLIGATION. Ex: they SHOULD recycle
more.

2. ABSENCEOF NECESSITY
 DON’THAVETO / DON’TNEED TO / NEEDN’T expresses it IS notnecessary ( PAST)
Ex: She NEEDN’T/ DOESN’TNEED TO/ DOESN’THAVETO pay for the ticket
 DIDN’TNEED TO/ DIDN’THAVETO expresses it WAS not necessary ( PAST)
Ex: He DIDN’TNEED TO / DIDN’THAVETO buy me a new dress.
 NEEDN’T HAVE+ PASTPARTICIPLE. Something was notnecessary BUTit was done.
Example: You NEEDN’THAVE BOUGHToranges ( but you did).
PROHIBITION
 MUSTN’T. It is forbidden to do something. Ex: You MUSTN’T smokehere
ADVICE
 SHOULD. General advice. You SHOULD usesolar power.
 OUGTH TO. General advice. You OUGHTTO usesolar power.