Choose the correct phrase to complete the detective's dramatic reveal.
I finally caught the thief! I _____ it was the butler since the very beginning of the investigation.
The correct answer is have known.
Even though the action started in the past and continues to the present (which often requires the Present Perfect Continuous), the verb know is a stative (state) verb. Stative verbs describe a state of being rather than a physical action, so they are rarely used in continuous tenses. Therefore, we must use the Present Perfect Simple (have known).
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.
Present tense
- I work here. — simple present (habit/permanent)
- I am working now. — present progressive (happening right now)
- I have lived here for 10 years. — present perfect (started past, still true)
- I have been waiting for an hour. — present perfect progressive (duration up to now)
Four present tense forms: simple (habits/facts), progressive (now/temporary), perfect (past → present relevance), perfect progressive (ongoing duration). Each encodes a different relationship between the action and the present moment.
Trap: "I am living here for 10 years" ❌ — started in the past + still true = present PERFECT (have lived/have been living), not progressive.
Perfect tense
- ✅ I have lived here for ten years. — present perfect (started past, still true)
- ❌ I live here for ten years. — wrong (simple present can't bridge past→now)
- ✅ She had finished before I arrived. — past perfect (earlier past)
- ✅ They will have left by noon. — future perfect (completed before future point)
The perfect = have + past participle. Connects an action to a reference point in time. Present perfect bridges past→now. Past perfect marks "earlier past." Future perfect marks "done before a future deadline."
Rule: if the action started in the past and is still relevant now → present perfect (have done). If two past events and you need the earlier one → past perfect (had done).
Simple tense
- ✅ I go to work every day. — present simple (habit)
- ✅ She went home yesterday. — past simple (completed action)
- ✅ I will call you later. — future simple (promise/decision)
- ✅ Water boils at 100°C. — present simple (general truth)
The simple aspect is the default, unmarked verb form. Present simple = habits, facts, schedules. Past simple = completed actions. Future simple = predictions, promises, decisions. No auxiliary needed (except will for future and do for questions/negatives).
Rule: if the action is a fact, habit, completed event, or scheduled future — and you don't need to emphasise it being in-progress or connected to now → simple tense.
Progressive tense
- ✅ I am working in London. — temporary, happening now
- ✅ I work in London. — permanent/habitual (simple)
- ❌ I am knowing the answer. — stative verb, can't be progressive
- ✅ She was reading when I arrived. — past progressive (in progress at that moment)
The progressive = be + -ing. Marks actions as ongoing, temporary, or in-progress at a reference time. NOT used with stative verbs (know, believe, own, want, like) unless meaning shifts.
Rule: is the action temporary/in-progress right now? → progressive. Is it a permanent fact, habit, or schedule? → simple. Is it a stative verb? → almost never progressive.
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.
Medium
- If I were you, I would apologise. — one rule (second conditional), but distractors like was tempt you
- Answers require active thought, not instant pattern recognition
- Vocabulary and context are realistic, not artificially simplified
- Usually tests one rule, but the wrong answers are plausible
Medium marks middle-difficulty challenges: A2–B1, one rule tested, but with realistic distractors that require genuine understanding.
Use "Medium" when Easy feels too obvious but Hard feels overwhelming. This is where most productive learning happens — the sweet spot of difficulty.