Modal verbs are verbs that indicate likelihood, ability, permission or obligation. Modal verbs change the intention or meaning of the main verb in a sentence by showing whether an action is: Learn ...
Modal verbs, which express a likelihood, ability, permission, request, order etc., usually help main verbs to state the future. It is the reason they are categorised as auxiliary verbs in the context.
Mea culpa, mea culpa, mea minima culpa: Michael Bulley (Letters, 10 May) is right to correct me – Latin does have the modal verbs he names, which cover possibility (possum), permission (licet) and ...