Hi! Saskia for BBC Learning English here,
and today I'm going to tell you about
how we use verbs of perception in English.
There are a number of these verbs
but I'm just going to look at two with you now:
see and hear.
When we use these verbs, this is the form:
First, the verb of perception.
Then, the object of the sentence.
Then we have either
the infinitive without to or the -ing form.
Here's an example: I heard him go down the stairs.
Or:
I heard him going down the stairs.
There's a slight difference between these two forms:
When we use the infinitive, it suggests that we hear or see
the whole action or event.
Using the -ing form suggests that we hear or see something in progress.
'I saw her cross the street'
means I saw her cross from one side to the other.
'I saw her crossing the street'
means I saw her in the middle - on the way across.