“Modal Auxiliaries: Any of the verbs that combine with the main verb to express necessity (must), obligation (should), permission (may), probability (might), possibility (could), ability (can), or tentativeness (would). Mary might wash the car.”
Excerpted from: Strunk, William Jr., and E.B. White. The Elements of Style, Fourth Edition. New York: Longman, 2000.
Mark's Text Terminal 