An introduction to modal verbs

What are modal verbs?

Modal verbs are a special class of verb in English that have four characteristics:

they modify the meanings of other verbs but do not have their own meaning
they are ‘defective’ – they do not have a present participle (-ing) or past particle (often -ed) form, an infinitive form (to + verb) and do not have an ‘s’ in the third person singular form (he/she/it)
the verb that they modify follows the modal verb in the bare infinitive (unconjugated without the preposition ‘to’) form
subject-verb inversion for questions and negatives (do not use the word ‘do’)

A modal verb also does something called “showing modality”. In simple terms, modality shows what someone believes, intends or wants. Some example of modal verbs include:

But what makes them different and how do you use them?

Let’s look at each point individually:

they modify the meanings of other verbs but do not have their own meaning

As was said before modal verbs do not have a true meaning of their own. This means that modal verbs always have to have another verb. They can never be used alone. You can’t say: I can German but rather I can speak German.

NOTE: there is an exception to this rule. When answering a question, for example:

Question: Can you tie a knot?
Positive answer: Yes, I can.
Negative answer: No, I can’t.

But why is this exception possible? In this case the rest of the sentence is implied. The full answer would be “Yes, I can tie a knot” or “No, I can’t tie a knot.”

they do not have a present participle (-ing) or past particle (often -ed) form – this is called ‘defective’

For a sentence, this means that you can never use another verb before a modal verb. They always come first. For example, you can never say: I am can go…

Finally:

the verb that they modify follows the modal verb in the bare infinitive (unconjugated without the preposition ‘to’) form

Since they have to come before other verbs, the verbs are used in the bare infinitive afterwards. For example: I must go to the bank. This is also true when you use a modal verb before a perfect construction: He must have gone to the bank. Note that the verb have is in the bare infinitive, which is then followed by the past participle.