I could startle you could startle he could startle we could startle you could startle they could startle
V-ing form
I could be startling you could be startling he could be startling we could be startling you could be startling they could be startling
Perfect
I could have startled you could have startled he could have startled we could have startled you could have startled they could have startled
V-ing perfect
I could have been startling you could have been startling he could have been startling we could have been startling you could have been startling they could have been startling
Negation
Simple form
I could not startle you could not startle he could not startle we could not startle you could not startle they could not startle
V-ing form
I could not be startling you could not be startling he could not be startling we could not be startling you could not be startling they could not be startling
Perfect
I could not have startled you could not have startled he could not have startled we could not have startled you could not have startled they could not have startled
V-ing perfect
I could not have been startling you could not have been startling he could not have been startling we could not have been startling you could not have been startling they could not have been startling
Interrogative form
Simple form
could I startle? could you startle? could he startle? could we startle? could you startle? could they startle?
V-ing form
could I be startling? could you be startling? could he be startling? could we be startling? could you be startling? could they be startling?
Perfect
could I have startled? could you have startled? could he have startled? could we have startled? could you have startled? could they have startled?
V-ing perfect
could I have been startling? could you have been startling? could he have been startling? could we have been startling? could you have been startling? could they have been startling?
Interro-negative form
Simple form
could I not startle? could you not startle? could he not startle? could we not startle? could you not startle? could they not startle?
V-ing form
could I not be startling? could you not be startling? could he not be startling? could we not be startling? could you not be startling? could they not be startling?
Perfect
could I not have startled? could you not have startled? could he not have startled? could we not have startled? could you not have startled? could they not have startled?
V-ing perfect
could I not have been startling? could you not have been startling? could he not have been startling? could we not have been startling? could you not have been startling? could they not have been startling?