English grammar - Roger Berry 2012

B6.1 Modality
B6 Modal auxiliaries
Section B Development

Modality is to do with the way statements are qualified by speakers to show that they are not facts, either because there is some personal element involved in their realisation, or because they are seen as lacking certainty.

You must do it.

It might rain.

Sentences without modality are presented as facts:

I saw him yesterday.

It’s raining.

All four open word classes can express modality. We have already discussed modal adverbs (such as probably) in B4; adjectives (It is probable that...), nouns (There is a probability that...) and verbs (It appears that...) can also express modality. However, in this section we are interested in the use of modal auxiliaries to express modality.