Should in an if-clause: If is omitted here, and should is moved to the beginning before the subject. It denotes an unlikely future outcome - compare the above with If the food gets cold before you are home, you can heat it up in the microwave. If + should + simple present verb / simple present in main sentence.
Auxiliary verb
Auxiliary vs main verb: a main verb carries the action (run, eat, think); an auxiliary verb carries the grammar — tense, negation, questions, aspect, voice. In She has been eating, eating is the main verb; has and been are auxiliaries.
The English auxiliaries are be, have, do (primary) and the modal verbs (can, will, must…). They always precede the main verb.
Diagnostic: can the word stand alone as the only verb in the sentence and still carry action? Yes → main verb. No → auxiliary.
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.
Verb tense
Tense vs aspect: tense locates the action in TIME (past/present/future). Aspect describes its SHAPE — is it completed (perfect), ongoing (progressive), or just a fact (simple)? English combines these independently: was working = past (tense) + progressive (aspect). Confusing tense with aspect is why the 12-form grid feels overwhelming.
Verb tense = 3 time references × 3 aspects = 12 forms. Tense says when; aspect says how the action unfolds relative to that time.
Diagnostic: wrong time? → tense error. Right time but wrong "shape" (e.g., I work here for ten years instead of I've worked)? → aspect error.
Subjunctive mood
Subjunctive vs indicative: indicative states facts (He goes every day). Subjunctive marks unreality (I suggest he go; If I were you). The subjunctive drops the -s and insists on were — signalling "this isn't (or may not be) real." In informal speech it's disappearing, but formal/academic writing still expects it.
The subjunctive mood = hypothetical/counterfactual marker. Present subjunctive (base form after suggest/demand/insist that). Past subjunctive (were in unreal conditionals).
Diagnostic: is the clause about something unreal, demanded, or recommended (not yet true)? → subjunctive. Is it factual? → indicative.
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.
C1 | Advanced
C1 vs C2: C1 means fluent and flexible use with occasional gaps in very unfamiliar domains. C2 means native-like command of idiom, irony, and register across any subject. If you can handle advanced grammar but still miss cultural nuance or very rare idioms, you're C1.
C1 is the advanced CEFR level: inversion, cleft sentences, subjunctive mood, advanced conditionals, and precise register control in professional and academic contexts.
Diagnostic: can you write persuasively in different registers and catch subtle irony? Consistently → C2. Sometimes → 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.