should

• 情态动词，表示建议、推荐、义务、期望或可能性；语气比 must 弱，常指道义上的应该或做某事的适宜性。

Modal auxiliary verb serving as the past tense and conditional form of 'shall', though 'should' has developed distinct semantic functions largely independent of 'shall' in modern usage. Primarily expresses advice, recommendation, moral obligation, expectation, or probability. Conveys weaker obligation than 'must' and more personal judgment than 'have to'. Used in conditional clauses (first/second conditionals), reported speech for backshifting 'shall', and to express regret about past actions ('should have + past participle'). Forms a functional gradient with 'must' (strong obligation) → 'should' (advisable) → 'could/might' (tentative). Also appears in formal subjunctive-like constructions ('I suggest that he should...') and rhetorical questions. Used consistently across all English varieties, though frequency and contextual preferences vary slightly between British and American English.

1. Advice or RecommendationB1formal

   Used to offer suggestions, recommendations, or advice about what is advisable, beneficial, or morally appropriate. 'Should' expresses the speaker's opinion about the optimal course of action without the force of obligation that 'must' carries. This is the most frequent and productive use of 'should' in contemporary English, common in everyday conversation, professional guidance, health advice, and educational contexts. The negative form 'should not/shouldn't' advises against an action. Related to 'ought to', which is slightly more formal and emphasizes moral duty.

   建议或推荐

   • You should drink plenty of water when exercising in hot weather.
   • Students should review their notes regularly to reinforce learning.
   • If you're feeling unwell, you should consult a healthcare professional.
   • We should consider alternative solutions before finalizing the decision.
   • You shouldn't ignore error messages; they often indicate important issues.

2. Expectation or Probable OutcomeB1formal

   Expresses that something is likely to happen or is expected based on logic, norms, schedules, or general knowledge. This epistemic use indicates moderate-to-high probability, stronger than 'might' but less certain than 'will'. Common in predictions, planning contexts, or statements about typical behavior. Often appears with time references ('should be here soon') or conditional premises ('If everything goes as planned, it should work'). The negative form 'shouldn't' expresses expectation that something will not occur.

   预期或可能的结果

   • The package should arrive by tomorrow afternoon if shipping proceeds normally.
   • With your qualifications, you should have no trouble finding a suitable position.
   • The meeting should start in ten minutes; let's take our seats.
   • This method should reduce processing time by approximately 30%.
   • He left an hour ago, so he shouldn't be far from the destination now.

3. Moral Obligation or Social NormB2formal

   Indicates what is morally right, socially appropriate, or ethically expected, reflecting shared values or normative standards rather than personal preference. This deontic use of 'should' conveys a sense of duty, responsibility, or propriety, though less absolute than 'must'. Common in discussions of ethics, citizenship, professional conduct, or interpersonal relationships. The negative form 'should not' expresses moral prohibition or social disapproval. Distinct from legal obligation (where 'must' or 'shall' is preferred) and from practical advice (where consequences, not morals, are emphasized).

   道德义务或社会规范

   • Citizens should vote in democratic elections to uphold representative governance.
   • Companies should prioritize environmental sustainability in their operations.
   • We should treat others with respect and empathy, regardless of differences.
   • Researchers should obtain informed consent before conducting human subjects studies.
   • You shouldn't spread unverified information on social media platforms.

4. Regret or Criticism about Past Actions (Should Have + Past Participle)B2formal

   Used in the perfect infinitive construction ('should have + past participle') to express regret, criticism, or retrospective judgment about actions that were not taken or were taken inappropriately in the past. This usage conveys that a different choice would have been preferable, advisable, or morally correct. Common in reflective discourse, feedback, self-evaluation, or narrative commentary. The negative form 'should not have' criticizes actions that were performed but are judged as mistaken or inappropriate. This structure is essential for discussing lessons learned, accountability, or hypothetical past alternatives.

   对过去行为的遗憾或批评（本应该 + 过去分词）

   • I should have started preparing for the presentation earlier; now I'm rushed.
   • They should have consulted the legal team before signing the agreement.
   • She shouldn't have ignored the warning signs; the problem was predictable.
   • We should have allocated more resources to testing before the product launch.
   • He should have apologized immediately instead of waiting for escalation.

5. Formal Subjunctive-Like or Mandative ConstructionsC1formalbritish

   Appears in formal or British English after verbs of suggestion, demand, recommendation, or necessity (e.g., 'suggest that...', 'insist that...', 'it is important that...') to express a proposed or required action. This usage functions similarly to the present subjunctive (bare infinitive without 'should'), with 'should' being more common in British English and the bare infinitive preferred in American English. The construction conveys that the action is advisable, necessary, or expected according to the speaker's stance or institutional norms. Less frequent in informal speech but essential for formal writing, academic discourse, and professional communication.

   正式虚拟语气或祈使性结构

   • The committee recommends that all members should attend the orientation session.
   • It is essential that the data should be verified before publication.
   • She insisted that he should receive formal recognition for his contributions.
   • The policy states that employees should report any safety concerns immediately.
   • I propose that the budget should be reallocated to prioritize research and development.