Here's why:
* Auxiliary Verbs: These verbs help main verbs to express things like tense, mood, and voice.
* Modal Verbs: These are a special kind of auxiliary verb that indicate likelihood, ability, permission, obligation, or necessity.
Examples:
* You ought to study for the test. (Indicates obligation)
* We ought to go to the beach. (Indicates suggestion or recommendation)
Key Features of Modal Auxiliaries:
* They are always followed by a main verb in its base form (e.g., "ought to *go*").
* They don't change their form to agree with the subject (e.g., "I ought to," "he ought to").