"Could" is used to make a polite request. The correct sentence is "Could you lend me a pen, please?"
Auxiliary verb
- ✅ Do you know? — ❌ Know you? (English requires do-support for questions)
- ✅ She has finished. — ❌ She finished has. (auxiliary before main verb)
- ✅ They are leaving. — ❌ They leaving. (progressive needs be)
- ✅ He doesn't smoke. — ❌ He smokes not. (negation needs do)
Auxiliary verbs (be, have, do, and the modals) combine with main verbs to build questions, negatives, tenses, aspects, and passive voice.
Pattern: if you need to ask a question, negate, or stack tense/aspect — you need an auxiliary. The main verb carries meaning; the auxiliary carries grammar.
Verb
- walk → walk / walks / walked / walked / walking (5 forms, regular)
- go → go / goes / went / gone / going (5 forms, irregular)
- be → am/is/are/was/were/be/being/been (8 forms)
- can → can / could (modal: only 2 forms, no -s, no -ing)
A verb is the one word class every English sentence requires. Carries tense (when), aspect (duration), mood (attitude), and voice (active/passive). Regular verbs add -ed; ~200 irregular verbs have unpredictable past forms.
Key insight: fix your verbs and most grammar problems disappear. Wrong tense, wrong agreement, wrong form — verb errors account for the majority of grammatical mistakes.
Modal verb
- ✅ She can swim. — ❌ She can to swim. (modal + bare infinitive, no to)
- ✅ You must leave now. — strong obligation
- ✅ It might rain. — possibility (~50%)
- ✅ He should apologise. — advice/recommendation
Modal verbs (can, could, may, might, must, shall, should, will, would) are auxiliaries expressing ability, permission, possibility, obligation, or speculation. Always + bare infinitive. Never inflected (she can, not she cans).
Rule: modals never take to after them, never add -s for third person, and can't combine directly (must can ❌ — use must be able to).
Questions
- ✅ Do you like coffee? — do-support (no existing auxiliary)
- ✅ Can she swim? — inversion (auxiliary before subject)
- ✅ Where does he live? — wh-question
- ✅ You're coming, aren't you? — tag question
Questions require inversion (auxiliary before subject) or do-support (add do/does/did). Types: yes/no (Do you…?), wh- (What/Where/When…?), negative (Don't you…?), tag (…isn't it?).
Rule: find the auxiliary. Move it before the subject. No auxiliary? Add do/does/did. Never use just intonation in written English (You like coffee? is not standard).
B1 | Intermediate
- ✅ If I had more time, I would travel more. — second conditional
- ✅ The bridge was built in 1920. — passive voice
- ✅ She said she was tired. — reported speech with backshift
- ✅ Although it rained, we enjoyed the trip. — complex sentence with concession
These are B1 patterns — the CEFR intermediate level. At B1 you link ideas, use passive voice, handle reported speech, and manage second conditional — enough for travel, work basics, and everyday independence.
Marker: if you can explain why something happened and follow a news story, you're B1.
Easy
- She is a teacher. — one verb form, one rule
- I have two cats. — basic possession, short sentence
- He doesn't like coffee. — simple negation with do-support
- Only one answer is clearly correct; distractors are obviously wrong.
Easy marks beginner-level challenges: A1–early A2, one rule at a time, everyday vocabulary, no trick questions.
Use "Easy" when you want to build confidence on a specific rule without interference from other grammar or tricky contexts.