Modality is an important technique for the expression of argument and
opinion in academic writing.
Modality can take various forms and be expressed in different ways.
For example, bi-modal verbs such as must and may, or marginals like need to.
Or, semi-modals, like have to.
And lexical words, for example, nouns, adjectives, adverbs, verbs and quantity.
The main forms of model auxiliary verbs are can, could,
may, would, might, will, must, should and ought to.
Each of these forms has a variety of functions and meanings, such as ability,
reassurance, requesting, controlling, certainty and so on.
This table illustrates some examples of forms and
functions in the use of modal verbs.
It is evident that modality is to be used very carefully in academic
communication because it has similar meanings and functions.
Very few ideas in academia can be stated as fact.
So using modality allows academic writers to express,
with various degree of certainty, ideas that are not facts.
Let's consider this example.
Climate change threatens the health of millions of people.
Definitely, this is a fact, because the verb is expressed by present simple tense
whose main function is to state facts.
Climate change might threaten the health of millions of people.
In this case, modality expresses low certainty.