Questions: Auxiliary Verbs and Modal Meaning

Question 1

Which of the following sentences contains a grammatical error in modal usage?

• A. She might arrive late tonight.
• B. They must to submit the form by Friday.
• C. He could help you if you asked.
• D. We should leave before the storm.

Answer: (B)

'Must to submit' is ungrammatical. Modal auxiliaries are always followed by a bare infinitive — the plain verb form without 'to'. The correct sentence is 'They must submit the form by Friday.' This distinguishes modals from semi-modals like 'have to' and 'be going to', which do require 'to'. The morphological invariance of modals — no -s, no -ed, no -ing, no 'to' — is their defining formal property.

Question 2

The sentence 'You can leave now' is ambiguous. What are the two possible readings?

• A. A past capability and a present capability
• B. A deontic reading (you have permission) and an epistemic reading (you are able)
• C. An obligation and a prohibition
• D. A question and a command

Answer: (B)

Modal verbs often carry both epistemic and deontic readings. Epistemic modality concerns what the speaker believes is possible or probable; deontic modality concerns permission, obligation, or necessity. 'Can' covers both: 'You can leave' might mean 'you have permission to leave' (deontic) or 'you are physically/logistically able to leave' (epistemic ability). Context — who is speaking to whom, and in what situation — resolves the ambiguity.

Question 3

Modal verbs like 'should' and 'can' can take an -ed ending to form past tenses, just like the primary auxiliaries 'be' and 'have'.

• T. True
• F. False

Answer: False

This is a defining property of modals: they are morphologically invariant. You cannot say 'she musted' or 'he canned.' Modals have no -s in third-person singular, no -ed past tense, no -ing progressive, and no bare infinitive 'to'. This distinguishes them from primary auxiliaries (be, have, do), which do inflect. For past or hypothetical meaning, modals pair with a past infinitive: 'she could have left' rather than 'she could-ed leave.'

Question 4

'You should submit your assignment by Friday' and 'You have to submit your assignment by Friday' are largely interchangeable — they convey identical meaning in most contexts.

• T. True
• F. False

Answer: False

'Must' typically carries the speaker's personal authority — it is the speaker imposing the requirement. 'Have to' points to an external obligation or rule that exists independently of the speaker. 'You must be quiet' is a personal command; 'You have to show your ID' invokes an institutional rule. The social texture differs even when the factual content is nearly the same: substituting one for the other can sound presumptuous or impersonal depending on context.

Question 5

What is the difference between epistemic and deontic modality? Give an example of a single modal sentence where context would determine which reading applies.

Model answer: Epistemic modality expresses the speaker's judgment about possibility, probability, or certainty ('It might rain' = I think this is possible). Deontic modality expresses permission, obligation, or necessity ('You might leave' in an older/formal register = you have permission). A sentence like 'You can use my computer' illustrates the ambiguity: in a practical context it likely means ability (epistemic), but from a supervisor or host it likely means permission (deontic). Context — especially the relationship between speaker and listener — resolves which reading applies.

The epistemic/deontic distinction captures the two main jobs modal verbs do: describing the world (how certain, how probable) versus regulating behavior (what is allowed, required, or necessary). Recognizing which job a modal is doing in context is essential for both accurate comprehension and natural production of the language.