Modal Verbs

Modals, words like might, may, can, could, will, would, must, and should are helping verbs that add shades of meaning or “flavor” to the verbs that follow them. This additional meaning may connote possibility, ability, and permission among others:






These responses might be inaccurate.




The importance of the effects may differ.

You may come in.




She can speak several languages.

They can start working on this issue now.


polite request

past ability



Could we meet tomorrow?

He could run faster when he was a child.

You could examine this issue in more detail.

This could be the optimal solution. 



polite request

The prices will go down.

Will you help me with this project?


offering, inviting

polite request

Would you join us for lunch?

Would you send your slides before the class?


advising, suggesting


Future policies should address this issue.

The weather should improve soon.


obligation, necessity


You must stop at the stop sign.

The new library is large. It must have many books

As the table shows, modals may have several meanings, and the same meaning can be expressed by different modals (e.g., may and can both express permission). Although generally modals with the same meaning can be used interchangeably, they express a slightly different degree of their meaning. As an example, the modals below are ranked according to the degree of certainty/probability:

strong degree of certainty/probability

⬆️    will rain               

        must rain

        should rain         

        may rain         

⬇️    could/might rain

weak degree of certainty/probability


Grammatical Form

Modals are a special type of verbs; they are followed by the base form of verbs (e.g. I should go, she must see, he can swim).

In addition to the simple form of modals, there are also other forms to express:

past time1: modal + have + Past Participle (e.g., may have submitted)

passive voice2: modal + be + Past Participle (e.g., could be explained)

action in progress now: modal + be + ing (e.g., may be working)

action in progress in the past: modal + have been + ing (e.g., might have been studying)

1 Can has two forms when used to express ability in the past:

1) could - for the action happening over a period of time: I could swim fast when I was a child.

2) was able to - if it was a single past action: I was able to submit the English paper on time. (=managed to do something)

2See the handout “Active and Passive Voice” for more information on this topic.


Modals in Academic Writing

General use: Research examining multiple papers reveals that modal verbs are commonly used in academic writing. In fact, they are the third most widely used verb structure after present simple and past simple tense.

Hedges/Boosters: Modals are often used in academic writing to soften, or “hedge”, claims and show tentativeness of result interpretations. Writers use hedges to avoid criticism for being radical or overconfident. Thus, instead of writing “The reason for this change is …”, academic writers may write “The reason for this change might/may/can/could be…”, showing that they admit that many other factors could have influenced the change.

On the other hand, “boosters” are used to strengthen statements when writers want to emphasize their certainty. Thus, must, should, and will can be used to produce such effect: “This will influence our understanding of…”

See the handout “Hedges: Softening Claims in Academic Writing”

Politeness in emails: Certain modals add politeness to speech or writing. This is especially important for writing emails to professors or colleagues since writers do not want to appear demanding or pushy. Using modals such as might, may, could, can, and would can help addressees perceive writers as friendly and polite.


Last updated 6/01/2018