In the English language, a modal verb is an auxiliary verb that can be used to change the modality of a sentence. The key way to identify a modal verb is by its defectiveness (they have neither participles nor infinitives). In addition, modal verbs do not take the inflection -s or -es in the third person singular, unlike other verbs.

The modal verbs in English are as follows, paired as present and preterite forms.

• shall and should
• will and would
• may and might
• can and could

The following have also been categorized by some as modal verbs:

• ought (to)
• had better
• dare

The following are not modal verbs although they have some similar characteristics:

• used to
• do
• be going to
• have to

Syntax

If a verb is preceded by multiple auxiliary verbs including a modal, as in "it could have been eaten," the modal will always appear before the other auxiliary verbs. A verb or auxiliary verb following a modal always appears in its basic form (for example, "could have gone" instead of "could had gone" or "could has gone", and "He could walk" rather than "he could walks").