Modal verbs are weird verbs because they don’t follow the regular rules - they’re rebels and outlaws! As such, we refer to them as “auxiliary verbs” because they need another verb to latch onto for meaning. They always express a hypothetical.

It’s the difference between

Examples include:
• I go to the library on Tuesdays.
• I can go to the library on Tuesdays.
• I could go to the library on Tuesdays.

The first indicates you actively go to the library on Tuesdays, while the second indicates your ability to go without a definite. The third shows the possibility of you being able to go. Can and Could are modals.

You don’t - you use them as-is. They don’t have a specific ending and don’t function in an infinitive form, but can alter the meaning of a sentence significantly. However, they ALWAYS need another verb and, as such, are often considered to be helping verbs.

It sounds more confusing than it actually is once you see what the verbs are. The chart below shows them in terms of the certainty they express. Either it shows the verb will definitely happen, or they indicate some degree of uncertainty.

There are several ways to use modal verbs depending on the meaning you wish to convey. Each modal can have multiple meanings depending on how it’s used in a sentence. Here are some examples of the different meanings of each of the major modal verbs.

Using modals depends on the tense and the amount of certainty you wish to convey. With practice, you’ll get the hang of using these oddball verbs.