Grammar (Tenses, Voice, Narration, Modals, Articles, Prepositions, Subject-Verb Agreement)
Core rules
- Tense: use the present perfect for an action whose exact time is not stated; use the past perfect for the earlier of two past actions.
- Voice: passive = a form of be + past participle; keep the original tense and make the object the new subject.
- Narration: with a past reporting verb, shift tense back one step and change pronouns and time/place words (now to then, today to that day).
- Modals: use modal + base verb; must for obligation, can for ability, may for permission or possibility.
- Articles: a/an before singular countable nouns; the for something already specified or unique.
- Prepositions: learn verb + preposition pairs such as depend on, listen to, and good at.
- Subject-verb agreement: the verb agrees with the subject, not with a phrase in between.
Worked example
Change to passive: "The teacher is correcting the answer sheets." Reasoning: The active form is present continuous. The passive pattern is is/are being + past participle. The object "the answer sheets" becomes the subject, so the verb becomes "are being corrected". Add "by the teacher" only if the doer matters. Answer: "The answer sheets are being corrected by the teacher." Check agreement: "answer sheets" is plural, so use are, not is.
Traps
- Changing the tense while changing the voice.
- Adding "by" when the agent is unknown or unimportant.
- In narration, forgetting that "said to" becomes "told".
- Writing double modals such as "can able to".
- Using "a" before a vowel sound or omitting "the" before a unique noun.
- Letting a phrase between subject and verb control agreement.