After a sensing verb such as "watch", we use an infinitive to mean that you have witnessed the entirety of an action.
Gerund
- ✅ I enjoy reading. — ❌ I enjoy to read.
- ✅ She's good at swimming. — ❌ She's good at to swim.
- ✅ He avoids making eye contact. — gerund after avoid
- ✅ Running is good exercise. — gerund as subject
A gerund is the -ing form of a verb functioning as a noun. It follows verbs like enjoy, avoid, finish, mind and ALL prepositions. Never use an infinitive where a gerund is required.
Rule: after a preposition (at, in, of, about, without) → always gerund. After enjoy, avoid, finish, mind, suggest, deny → always gerund.
Infinitive
- ✅ I want to go. — to-infinitive after want
- ✅ She can swim. — bare infinitive after modal
- ✅ Let me help. — bare infinitive after let
- ❌ I enjoy to read. — wrong (enjoy takes gerund, not infinitive)
The infinitive has two forms: to-infinitive (to go) after verbs like want, decide, plan, hope; bare infinitive (go) after modals and causatives (let, make, help).
Rule: after want, need, decide, plan, hope, expect, agree, refuse → to-infinitive. After can, will, must, let, make → bare infinitive. After enjoy, avoid, finish → gerund, NOT infinitive.
A2 | Elementary | Pre-intermediate
- ✅ I went to the cinema yesterday. — past simple
- ✅ I have visited Paris twice. — present perfect (life experience)
- ✅ If it rains, I'll take an umbrella. — first conditional
- ✅ You should see a doctor. — modal for advice
These patterns are A2 — the second CEFR level. At A2 you move past survival phrases into real grammar: past tenses, the present perfect, basic conditionals, and modals for advice/obligation.
Marker: if you can describe yesterday and give simple advice, but struggle with abstractions or nuance, you're at A2.
Hard
- Had she not intervened, the situation would have escalated. — inverted conditional
- All distractors are grammatically plausible in other contexts
- Multiple rules interact (e.g., tense + aspect + modality)
- Context determines the answer — no single "rule" is enough
Hard marks upper-intermediate to advanced challenges: B2+, interacting rules, edge cases, plausible distractors, and contexts where pattern-matching fails.
Use "Hard" when Easy/Medium feel trivial and you want to test whether you actually understand a rule versus just recognising surface patterns.