Tense, Aspect & Modal Verbs: Rules, Uses & NEB Exam Tricks

TAKEAWAYS:

• Tenses show when an action happens (past, present, future), while aspects (continuous/perfect) show how it happens (ongoing, completed).
• Simple tenses (e.g., I eat) describe habits or general truths; continuous tenses (e.g., I am eating) describe actions in progress.
• Perfect tenses (e.g., I have eaten) link past actions to the present; perfect continuous (e.g., I have been eating) shows duration.
• Modal verbs (can, must, should) express ability, permission, obligation, or possibility—never take -s or -ed endings.
• Common NEB mistakes: Mixing since (point in time) with for (duration), or using will for fixed future plans (use am/is/are going to instead).
• Exam trick: Spot time clues (yesterday, now, tomorrow) to pick the right tense, and modal verb patterns (e.g., must have + past participle for deduction).

1. What Are Tenses, Aspects, and Modal Verbs?

English verbs change form to show time (tense), how the action happens (aspect), or attitude toward the action (modal verbs).

• Tense: Past (ate), Present (eat), Future (will eat).
• Aspect: Shows if the action is ongoing (continuous) or completed (perfect).
  • I am eating (ongoing now) vs. I have eaten (finished, but affects now).
• Modal Verbs: Can, may, must, should etc. They do not change (no -s or -ed) and are always followed by the bare infinitive (to eat → eat).

2. The 12 English Tenses (Simple, Continuous, Perfect, Perfect Continuous)

NEB exams test your ability to identify and use these correctly. Here’s a breakdown:

A. Simple Tenses (No Aspect)

Used for habits, general truths, or single actions.

Worked Example:

• Incorrect: Yesterday, I go to school. (Wrong tense)
• Correct: Yesterday, I went to school. (Past Simple)

B. Continuous (Progressive) Tenses (Ongoing Actions)

Used for actions happening at a specific time or temporary situations.

Worked Example:

• Incorrect: Right now, she reads a book. (Present Simple for a current action is wrong)
• Correct: Right now, she is reading a book. (Present Continuous)

NEB Common Mistake: ❌ I am knowing English. (Wrong: know is a stative verb—use Present Simple: I know English.) ✅ Stative verbs (know, like, want, believe) do not use continuous tenses.

C. Perfect Tenses (Completed Actions with Present/Past/Future Link)

Used for actions completed before another time or experiences up to now.

Worked Example:

• Incorrect: She has gone to school yesterday. (Wrong: yesterday is a past time → use Past Simple)
• Correct: She went to school yesterday. (Past Simple)
• Correct for Present Perfect: She has gone to school. (Action completed, but result affects now—e.g., she’s not here anymore.)

Time Clues for Perfect Tenses:

• Present Perfect: ever, never, already, yet, recently, so far, up to now
  • Have you ever eaten momo?
• Past Perfect: before, after, by the time, when
  • By the time I arrived, the movie had started.

D. Perfect Continuous Tenses (Duration of Actions)

Used for how long an action has been happening (with since or for).

Worked Example:

• Incorrect: I have been knowing her for 5 years. (Wrong: know is stative → use Present Perfect Simple: I have known her for 5 years.)
• Correct for actions: I have been learning English since 2020. (Ongoing action)

NEB Exam Tip:

• Since = point in time (since 2010, since Monday)
  • I have lived here since 2015.
• For = duration (for 5 years, for a long time)
  • I have lived here for 5 years.

3. Modal Verbs: Meaning and Use

Modal verbs (can, could, may, might, must, shall, should, will, would, ought to) express ability, permission, obligation, or possibility. They never change (no -s or -ed) and are followed by the bare infinitive (to eat → eat).

classDiagram
  class ModalVerbs {
    +can: ability/permission
    +may: polite request/possibility
    +must: strong obligation
    +should: advice/recommendation
    +might: weak possibility
    +need: necessity (negative/question)
    +ought to: strong advice
  }
  ModalVerbs --> "Bare Infinitive (V1)" : "Always followed by"
  ModalVerbs --> "No -s/-ed" : "Never changes form"
  ModalVerbs --> "Time Clues" : "e.g., *must have + V3* for deduction"

Worked Examples:

1. Ability:
   • I can speak English. (Present)
   • I could swim when I was young. (Past)
2. Permission:
   • Can I borrow your pen? (Informal)
   • May I leave early? (Formal)
3. Obligation:
   • You must submit the assignment on time. (Strong)
   • You should call your parents. (Weaker advice)
4. Deduction:
   • She must have left. (She is not here now.)
   • She might have forgotten. (Uncertain)

NEB Common Mistakes: ❌ She can goes to school. (Wrong: can is modal—no -s or -ed) ✅ She can go to school. ❌ I must to finish this. (Wrong: Modals are followed by bare infinitive, not to + V) ✅ I must finish this.

4. Comparison Table: Tenses and Aspects

5. How to Choose the Right Tense

Ask yourself:

1. When? (Past/Present/Future)
2. Is it ongoing? (Continuous)
3. Is it completed? (Perfect)
4. Is it a habit, fact, or single action? (Simple)

Example Sentence: "She ___ (cook) dinner when I ___ (arrive)."

• She was cooking dinner when I arrived.
  • Was cooking = Past Continuous (ongoing action)
  • Arrived = Past Simple (interrupting action)

6. Modal Verbs: Special Patterns

Exam Tip: NEB-Style Questions and How to Score Full Marks

NEB exams test identification, correction, and usage of tenses and modals. Here’s how to ace them:

A. Fill in the Blanks (Direct/Indirect Speech)

Question: She said, "I am happy." Rewrite in Indirect Speech. Answer: She said that she was happy. Why? Past tense in reported speech changes am → was.

Another Example: He said, "I have finished my work." → He said that he had finished his work.

B. Correct the Errors

Question: Yesterday, I am going to the market. Answer: Yesterday, I went to the market. Why?

• Yesterday = past time → Past Simple (went).
• Am going = Present Continuous (wrong for past).

C. Choose the Correct Option

Question: By next month, I ___ my exam. A) will take B) will have taken C) am taking Answer: B) will have taken Why?

• By next month = future time → Future Perfect (will have taken).

D. Rewrite Using Modal Verbs

Question: It is possible that she is sick. Rewrite using might. Answer: She might be sick.

E. Common NEB Exam Patterns

1. Time Clue Matching:

   • Since 2010 → Present Perfect (have/has + V3)
   • For 5 years → Present Perfect Continuous (have/has been + V-ing)

2. Modal Verb Deduction:

   • The light is on. Someone ___ home. A) must be B) can be C) may be Answer: A) must be (strong deduction).

3. Direct/Indirect Speech:

   • He said, "I will call you." → He said that he would call me.

Practice Questions (NEB Style)

Section A: Fill in the Blanks

1. She ___ (live) here since 2015. (Present Perfect Continuous)
2. By 2025, I ___ (work) here for 10 years. (Future Perfect Continuous)
3. ___ you ___ (see) that movie yet? (Present Perfect)
4. They ___ (watch) TV when the power went off. (Past Continuous)
5. You ___ (must) submit the assignment on time. (Obligation)

Answers:

1. has been living
2. will have been working
3. Have... seen
4. were watching
5. must

Section B: Correct the Errors

1. He is knowing English. → He knows English. (Stative verb)
2. I have been knowing her for 5 years. → I have known her for 5 years. (Stative verb)
3. She can goes to school. → She can go to school. (Modal verb + bare infinitive)
4. They was playing when I called. → They were playing when I called. (Past Continuous)
5. By next year, I will have worked here for 5 years. → By next year, I will have been working here for 5 years. (Future Perfect Continuous)

Section C: Rewrite Using Modal Verbs

1. It is necessary that you attend the meeting. → You must attend the meeting.
2. It is possible that she will be late. → She might be late.
3. You are not allowed to smoke here. → You must not smoke here.

Final Tip for NEB Exams:

• Read the question carefully—time clues (yesterday, now, tomorrow) decide the tense.
• Modals never take -s or -ed. Always follow with the bare infinitive.
• Stative verbs (know, like, want) do not use continuous tenses.
• Perfect tenses link past actions to now or another time (have/has + V3).
• Continuous tenses show ongoing actions (am/is/are + V-ing).

Good luck! Practice these patterns daily, and you’ll score full marks in the NEB exam. 🚀