One group of verbs connected with observation, e.g.
see, observe, sense, feel, hear, watch, perceive, can be followed by either
-ing or
a bare infinitive:
- I noticed him sneak out at lunchtime.
- I noticed him sneaking out at lunchtime.
- We heard the alarm bell ring and rushed out to see what was happening.
- We heard the alarm bell ringing and rushed out to see what was happening.
We normally use a bare infinitive when the action is completed. We use the
-ing form when the action is still in progress, which is similar to Continuous tenses.
Note that in corresponding passive structures, the bare infinitive is replaced with a to-infinitive.
- He was noticed to sneak out at lunchtime.
- He was noticed sneaking out at lunchtime.
- The alarm bell was heard to ring, and we rushed out to see what was happening.
- The alarm bell was heard ringing, and we rushed out to see what was happening.