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Using have to, be able to, be supposed to, had better, used to and similar expressions.
Semi-modal verbs are expressions that share some meanings or functions with core modal verbs but have different grammatical properties.
Common semi-modal expressions include have to, need to, be able to, be allowed to, be supposed to, ought to, had better, used to, and dare to.
Have to expresses necessity or obligation and behaves grammatically more like an ordinary verb than a core modal.
It can take different tenses and uses do-support in questions and negatives. For example, I have to leave, Did you have to leave?, and I do not have to leave.
Need to expresses necessity and is commonly used in everyday English.
For example, You need to call her and We need to leave soon.
Be able to expresses ability in grammatical contexts where can cannot normally be used.
For example, I will be able to help, She has been able to finish, and We hope to be able to come.
Be allowed to expresses permission and can be used in different tenses.
For example, We are allowed to park here, We were allowed to enter, and They will be allowed to vote.
Be supposed to expresses expectation, arrangement, duty, or what is generally considered correct or intended.
For example, You are supposed to wear a badge and The train is supposed to arrive at six.
Be expected to expresses an expectation about behaviour or an event.
For example, Students are expected to complete the assignment and Prices are expected to rise.
Had better expresses strong advice, often with an implication that an undesirable consequence may follow otherwise.
For example, You had better leave now and We had better take an umbrella.
Had better and should can both give advice, but had better is usually stronger and more closely connected to a particular situation or consequence.
Compare You should see a doctor with You had better see a doctor before the clinic closes.
Ought to expresses advice, expectation, or what is considered appropriate or probable.
For example, You ought to apologize and The package ought to arrive tomorrow.
Used to describes past habits or past states that are no longer true or no longer occur.
For example, I used to live in London and We used to play football every Sunday.
Negative and interrogative forms of used to vary by structure and dialect.
Common forms include Did you use to live here? and I did not use to like coffee. Usedn't you to... also occurs in some varieties of English.
Dare can behave either as an ordinary verb or, in some structures, as a marginal modal.
For example, I do not dare to ask is an ordinary verb pattern, while How dare you speak to me like that? shows marginal-modal behaviour.
Need can function as a marginal modal, especially in negative and interrogative constructions.
For example, Need I say more? and You need not worry. In everyday English, need to and do not need to are generally more common.
Need not and do not need to both express lack of necessity, but they differ in grammatical form and register.
Need not is more formal in many contexts, while do not need to is very common in everyday English.
Have got to can express strong necessity or obligation, especially in informal spoken English.
For example, I have got to leave now. It usually refers to present or near-future necessity.
Have to and have got to can both express necessity, but have got to is generally more conversational and has a more restricted tense system.
Compare I have to work tomorrow with I have got to work now.
Be going to can express a planned intention or a prediction based on present evidence.
For example, I am going to call her and Look at those clouds; it is going to rain.
Be likely to expresses probability and is often used as an alternative to a modal verb.
For example, She is likely to arrive soon and Prices are likely to increase.
Be unlikely to expresses low probability.
For example, They are unlikely to agree and The project is unlikely to finish on time.
Be bound to expresses a strong expectation that something will happen or be true.
For example, You are bound to make mistakes when learning a language.
Be due to can indicate that something is scheduled or expected to happen at a particular time.
For example, The train is due to arrive at six and The report is due to be published tomorrow.
Many semi-modal expressions can be changed into different tenses because they contain forms of be, have, or other ordinary verbs.
For example, had to, will have to, was able to, had been able to, and was supposed to.
Semi-modals share modal meanings with core modals but differ in their syntax and inflection.
For example, have to takes do-support, while must does not; be able to can take different tenses, while can cannot.
Different semi-modal expressions have different levels of formality and frequency.
Have to, need to, and be able to are extremely common, while ought to, need not, and dare in marginal-modal use are more restricted.
Use semi-modal expressions with the correct auxiliary, infinitive, tense, and meaning.
Common mistakes include confusing have to with must, using incorrect forms after had better, confusing used to with be used to, and treating every semi-modal as if it behaved like a core modal.