This document discusses various modal auxiliaries in English including can, could, may, might, must, should, and ought to. It provides examples of how each modal auxiliary is used to express ability, possibility, requests, permission, necessity, obligation, advice, deductions and prohibitions. It also notes that modal verbs do not accept other auxiliaries like do/does and do not receive an 's' in the third person singular. Finally, it discusses how to express future or past possibility or necessity using modal auxiliaries combined with will/would or was/were able to and had to.