Fill in the blank with correct modal auxiliary :
All men _______ die. (certainty)

Question

Accepted Answer

The correct option is 2:

**Detailed Explanation of Why 'Must' is Correct:**

The question asks you to fill in the blank with the modal auxiliary that conveys **certainty**. Modal auxiliaries, or modals, are helping verbs that express concepts like possibility, ability, permission, obligation, and necessity. Among the modals, **must** is the strongest way to express certainty, especially when referring to an inevitable truth, an undeniable fact, or a logical conclusion that is absolutely certain to happen.

The statement "All men \_\_\_\_\_\_\_ die" refers to a universal and unavoidable truth—mortality. This statement is not about a strong recommendation or a potential future action; it is a fundamental law of existence. Therefore, the modal verb used must reflect absolute, indisputable certainty. **Must** is the only option provided that carries this specific degree of inevitable obligation or certainty, fitting the context perfectly. When we say "All men must die," we are asserting a universal certainty, which aligns precisely with the required function given in the parenthesis: (certainty). The resulting sentence is grammatically correct and logically sound, expressing a timeless truth with the necessary force of inevitability.

**Explanation of Why the Other Options are Incorrect:**

The incorrect option is 1:

**Can** primarily expresses ability or possibility. For instance, "He can run fast" (ability) or "It can rain tomorrow" (possibility). While mortality is a possibility, "can" weakens the statement from a certainty to a mere ability or a general possibility, which is insufficient for a universal truth like death. It does not convey the absolute, unavoidable nature required by the context of certainty.

The incorrect option is 3:

**Should** is used to express a recommendation, a duty, or a strong piece of advice (obligation or desirability). For example, "You should study harder." If we used "should" in the sentence, it would suggest that dying is merely advisable or a moral duty for men, which is nonsensical in this context. It completely fails to convey the required sense of inevitable certainty.

The incorrect option is 4:

**Used to** is not a pure modal auxiliary; it is a semi-modal verb used only to express habitual actions or states that existed in the past but no longer exist now. For example, "I used to live there." Since the inevitability of death is a present and future certainty, not a discontinued past habit, "used to" is contextually and grammatically incorrect for this sentence.