English — Verbs of perception + do/doing
After see, hear, watch, feel, notice you can use object + bare infinitive or object + -ing. The bare infinitive (I saw him leave) presents the whole, completed action; the -ing form (I saw him leaving) presents the action in progress, as it was happening.
How it works
Use the bare infinitive when you saw the whole event from start to finish: I watched her cross the road (she reached the other side). Use -ing when you saw only part of it, in progress: I watched her crossing the road (she was in the middle of it). Compare I heard someone shout with I heard someone shouting.
Examples
| Bare infinitive — whole action | -ing — action in progress |
|---|---|
| I saw him leave. | I saw him leaving. |
| We heard the bomb explode. | We heard the bomb exploding. |
| She watched the plane take off. | She watched the plane taking off. |
| I felt the ground shake. | I felt the ground shaking. |
| They noticed him walk in. | They noticed him walking in. |
| I heard her sing a song. | I heard her singing in the garden. |
Good to know
Never insert to after these verbs of perception: say I saw him leave, not I saw him to leave. But in the passive the to reappears: He was seen to leave. Note the difference from causatives — with see/hear you keep the bare infinitive, unlike verbs such as want (I want him to leave).