11. Use of Modals

Mistakes in the use of English modal verbs—such as can, could, must, should, and might—often involve incorrect verb forms and misused meanings. A common error is adding an "s" or past-tense ending directly to the modal, like writing *he cans* or *she musted*. Another frequent mistake is following a modal with the "to-infinitive" instead of the base verb, such as *you should to go*. Finally, learners sometimes mix up modals of obligation and permission, confusing what is strictly required with what is merely optional or polite.