Form: If + Past Perfect, ...would have + Past Participle.

Use: To imagine a different past, often to express regret (If I had studied harder...) or criticism (If you had told me...).

Contractions: Natural speech uses contractions like If I'd known... and I would've helped....

be used to + noun/gerund: Describes the state of being familiar or accustomed to something (e.g., I am used to the cold weather.).

get used to + noun/gerund: Describes the process of becoming familiar with something (e.g., It took a while, but I got used to waking up early.).

Contrast: Differentiate these from used to + verb (a discontinued past habit).

Purpose: The information is "extra" and can be removed without losing the sentence's core meaning. Commas (or pauses in speech) are required.

Pronouns: Use who, which, whose, where. That cannot be used.

Example: My brother, who lives in London, is a doctor. (This implies the speaker has only one brother, and the location is extra information).

Present Obligation/Prohibition: must (strong internal obligation), have to (external rule), mustn't (prohibition).

Past Obligation: had to is the past of both must and have to.

Permission: can, could, and be allowed to for permission (I was allowed to leave early.).

Present Deduction: must be (95% sure it's true), can't be (95% sure it's impossible), might/could be (possible).

Past Deduction: must have / can't have / might have + Past Participle.

Structure is Key: The choice of be or have + P.P. determines whether the deduction is about the present or the past.

Tense "Backshift": The verb tense in the reported clause usually moves one step back into the past (e.g., is → was; went → had gone).

Contextual Changes: Pronouns (I → he/she) and words referring to time/place (tomorrow → the next day) must be changed logically.

Reporting Questions: Use if/whether for yes/no questions and a Wh-word for others, then change the question to statement word order (no inversion).

Reporting Commands/Requests: Use a reporting verb (told, asked, ordered) + object + infinitive (e.g., "Close the door." → He told me to close the door.).

Reporting Verbs + Gerund: Certain verbs are followed by a gerund (-ing) in reported speech (e.g., She suggested going to the cinema.).

Reporting Verbs + Infinitive: Other verbs are followed by an infinitive (e.g., He offered to help me. / He refused to go.).

Continuous Passive: be + being + Past Participle (e.g., The road is being repaired.). Focuses on an ongoing passive action.

Perfect Passive: have/has/had + been + Past Participle (e.g., The email has been sent.). Focuses on a completed passive action with current relevance.

Modal Passive: modal verb + be + Past Participle (e.g., This form must be signed.).

Wish about the Present/Future: I wish / If only + Simple Past (e.g., I wish I had more free time.).

Regret about the Past: I wish / If only + Past Perfect (e.g., If only I had studied harder for the test.).

Complaint/Annoyance: I wish + subject + would + base verb (e.g., I wish you would stop making that noise.).

Memory: remember/forget to do (refers to the future) vs. remember/forget doing (refers to a past memory).

Stopping: stop to do (interrupt one action to start another) vs. stop doing (quit an activity permanently or temporarily).

Effort vs. Experiment: try to do (make an effort, attempt something difficult) vs. try doing (do an experiment to see the result).