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Help the clumsy time traveler complete his diary entry about accidentally changing history.
Looking back, I realize I ____________________________________________ a neon tracksuit during my undercover mission to the Renaissance. Furthermore, Leonardo da Vinci _________________________________________ to paint his masterpiece if I hadn't spilled my futuristic, glowing sports drink all over his blank canvas.

...I ought not to have been wearing a neon tracksuit... Leonardo da Vinci might never have been inspired...

ought not to have been wearing: To express regret about an ongoing past action using "ought," the correct negative form is ought not to have been + -ing. Placing "not" after "to" (ought to not...) is grammatically incorrect.

might never have been inspired: This uses a past modal in the passive voice (might have been + past participle) to describe a hypothetical possibility in the past, matching the third conditional "if" clause that follows it.

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Modal verb

Must vs should vs might: the most confused modal trio. Must = strong obligation/near-certainty. Should = advice/expectation. Might = possibility. Getting these wrong changes the force of your statement: You must see a doctor (urgent) vs You should see a doctor (advice) vs You might need a doctor (maybe).

Modal verbs are auxiliaries that encode modality: ability (can), permission (may), necessity (must), advice (should), possibility (might), future (will).

Diagnostic: what meaning are you adding? Obligation → must/have to. Advice → should. Possibility → might/could. Ability → can. Future → will.

Past tense

Simple past vs past perfect: simple past puts events on the main timeline (I arrived. She left.). Past perfect marks an event as earlier than another past event (She had left before I arrived). If all events are in sequence, simple past is enough. Only use past perfect when you need to show "earlier than the main story."

The past tense has four forms encoding different temporal relationships: simple past, past progressive, past perfect, past perfect progressive.

Diagnostic: are events in sequence? → simple past is fine. Need to show one event happened before another past event? → past perfect for the earlier one.

Perfect tense

Present perfect vs simple past: I lost my keys (past: specific time, done). I have lost my keys (perfect: result matters NOW — I still don't have them). The perfect always connects past action to present relevance. If the time is specified (yesterday, in 2010) → simple past. If the result matters now → present perfect.

The perfect aspect = have + past participle. Marks completion relative to a time point. Three forms: present/past/future perfect.

Diagnostic: does the sentence mention a specific finished time (yesterday, last year, in 1999)? → simple past. Is it about the result/relevance NOW? → present perfect.

Passive voice

Active vs passive: active puts the doer first (The dog bit the man). Passive puts the receiver first (The man was bitten by the dog). Neither is inherently wrong — choice depends on what you want to foreground. Scientific/formal writing uses passive deliberately; vague writing uses it accidentally.

Passive voice = be + past participle. Promotes the object to subject. Good for foregrounding the action/result; bad when it hides who's responsible.

Diagnostic: who's doing the action? If unnamed and that matters → bad passive. If unnamed because it's obvious or irrelevant (The building was constructed in 1920) → good passive.

Conditional sentence

Second vs third conditional: second = unreal present/future (If I had money, I would buy it — but I don't have money now). Third = unreal past (If I had studied, I would have passed — but I didn't study). The most common confusion: using second when you mean third, making your timeline unclear.

A conditional sentence = if-clause + consequence clause. Five patterns (zero, 1st, 2nd, 3rd, mixed) each encode a specific time and probability.

Diagnostic: is the hypothetical about now or then? Now → second conditional. A past event that didn't happen → third conditional.

C2 | Proficiency

C2 vs C1: C1 is fluent and effective but occasionally reaches for words or misses cultural nuance. C2 is indistinguishable from a well-read native speaker — idiom, irony, register-switching all land naturally. Most learners never need C2; knowing it exists prevents over-ambition.

C2 is the highest CEFR level: full mastery of idiom, irony, allusion, and rhetorical control across all registers and subjects.

Diagnostic: could your writing pass as a native speaker's in any context — journalism, academia, comedy, legal? Yes → C2. Almost → still C1.

Hard

Hard vs Medium: Medium tests one rule with realistic distractors. Hard tests interacting rules, edge cases, or context-dependent answers where multiple options seem correct until you think deeply. If you're scoring 80%+ on Medium, try Hard to find your real gaps.

The Hard tag filters for B2+ challenges with layered difficulty: rule interactions, subtle distractors, and contexts that demand genuine grammatical reasoning.

Diagnostic: if Hard questions feel impossible, drop to Medium and master the individual rules first. Hard assumes you already know each rule — it tests whether you can apply them together.