English, German and Spanish grammar, quizzes and linguistic knowledge

Modal verb ‘must’ (forms & substitute)

Forms and substitute of ‘must’ in all tenses

(Overview of the modal verb ‘must’ in all tenses)

Contents

  1. General information
  2. Verb forms in the tenses
    1. Present tense forms
    2. Past tense forms
    3. Future tense forms
  3. Infinitives and imperatives

Particularities of the verb forms

  1. ‘must’ is a modal verb and can be only an auxiliary verb.
  2. It has just one single form in the present tense. For the other tenses, the substitute form ‘to have to’ needs to be used, which follows the conjugation pattern of ‘to have’.
  3. Grammatically, the direct negation of ‘must’ is ‘must not’, but the meaning changes to ‘not to be allowed to’!

Forms of the modal verb ‘must’ in all tenses

The verb ‘must’ in its original form can only appear in the present simple. To express all other tenses, the substitute form ‘to have to’ has to be utilized. However, modal auxiliary verbs like ‘must’ can never occur in the continuous or progressive aspect. The tables also highlight the particular forms that differ from the repeating ones. For clarification, the grammatical persons are presented as follows:

Number Person
Singular 1 I
2 you
3 he, she, it
Plural 1 we
2 you
3 they

Forms in the present

Tense Person and subject Simple Substitute form
Present 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 must have to
have to
has to
have to
have to
have to
Present perfect 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → have had to
have had to
has had to
have had to
have had to
have had to
  • Information: For negations, ‘not’ is placed after the verb (→ must not) or directly appended to construct the short form (→ mustn’t). Pay attention to the difference in meaning between ‘must’ and ‘mustn’t’.

Forms in the past

Tense Person and subject Simple Substitute form
Past 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → had to
Past perfect 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → had had to

Forms in the future

Tense Person and subject Simple Substitute form
Future (will) 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → will have to
Future (going to) 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → am going to have to
are going to have to
is going to have to
are going to have to
are going to have to
are going to have to
Future perfect 1 I
2 you
3 he, she, it
1 we
2 you
3 they		 only substitute form → will have had to

Infinitives and imperatives of ‘must’

The imperative expresses commands and generally exists only in the 2nd person singular and plural. As ‘must’ is limited in its forms, it does not have an imperative either:

Person and subject Imperative (affirmative) Imperative (negated)
2 you
2 you		 –
–		 –
–

The infinitive is the base form and, like the participles, appears in different aspects. Here, ‘must’ is similarly restricted and requires its substitute form:

Verb form (aspect) Infinitive Present participle Past participle
Simple must having to had to
Progressive –  – –
Perfect to have had to  having had to
(perfect participle)		 –
Perfect progressive – – –
  • Information: Although there is no proper progressive form of ‘must’, the auxiliary verb may be combined with a main (lexical) verb in the continuous form (the progressive aspect of modal verbs: must be waiting).
  • Here, too, ‘must’ cannot directly be used in the perfect tense but only its substitute. A combination with another verb in the perfect tense is possible, but the meaning may change (see the perfect aspect of modal verbs: must have been).