This document discusses the structure and uses of modal verbs in English. It outlines the rules for their structure, including that they do not take suffixes, are followed by the bare infinitive, and come before the subject in questions. It then discusses their common uses to express obligation, necessity, absence of necessity, prohibition, and advice. The main uses covered are must and have to for obligation, should/ought to for weak obligation, don't have to for absence of necessity, mustn't for prohibition, and should for advice.

1. MODAL VERBS
STRUCTURE
1- DO NOT TAKE-S, -ING,OR-ED SUFFIXES
( shouldS shouldEDshouldING are notcorrect)
2- FOLLOWED BY THE BARE INFINITIVE( INFINITIVEWITHOUT TO)
( SHOULD TO DO isnot correct)
3- COME BEFORE THE SUBJECT IN QUESTIONSAND ARE FOLLOWED BY NOT IN NEGATIONS.Example: MUST I
do this? No,you MUSTN’T do it
4- THEY DO NOT HAVETENSES IN THE NORMAL SENSE( I WILL MUST isnot correct,I am MUSTING is not
correct)
5- THEY ARE FOLLOWED BY A PRESENT BARE INFINITIVEWHEN THE REFER TO AN INCOMPLETE ACTION OR
STATE.
a. We SHOULD STOP the show( Present)
b. You SHOULD BE STUDYING more ( Presentcontinuous)
6- THEY ARE FOLLOWED BY A PERFECT BARE INFINITIVETOREFER TO A COMPLETE ACTION ORSTATE.
a. They SHOULD HAVERUN more today
b. TheySHOULD HAVEBEEN STUDYING more today.
USES ( MODALITY)
OBLIGATION / DUTY / NECESSITY
 MUST expressesDUTYor STRONG OBLIGATION.Ex:I MUST helpmybrother.
 HAVETO expressesSTRONGNECESSITY/OBLIGATION. Ex: I HAVETO studyharder.
 HAD TO is the past formof MUST andHAVE TO. Ex: I HAD TO helpmybrotherto studymaths.
 SHOULD/ OUGHT TO expressDUTY, WEAKOBLIGATION.Ex: theySHOULD recycle more.
ABSENCE OF NECESSITY
 DON’THAVE TO / DON’TNEED TO / NEEDN’T expresses itISnotnecessary( PAST)
Ex: She NEEDN’T / DOESN’TNEED TO/ DOESN’THAVE TO payfor the ticket
 DIDN’TNEED TO/DIDN’T HAVETO expressesitWASnotnecessary( PAST)
Ex: He DIDN’TNEED TO / DIDN’THAVETO buy me a new dress.
 NEEDN’THAVE + PAST PARTICIPLE.SomethingwasnotnecessaryBUT itwas done.
Example:YouNEEDN’THAVE BOUGHT oranges( but youdid).
PROHIBITION
 MUSTN’T. It is forbiddentodosomething. Ex:YouMUSTN’T smoke here
ADVICE