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 couldn't startle you couldn't startle he couldn't startle we couldn't startle you couldn't startle they couldn't startle
V-ing form
I couldn't be startling you couldn't be startling he couldn't be startling we couldn't be startling you couldn't be startling they couldn't be startling
Perfect
I couldn't have startled you couldn't have startled he couldn't have startled we couldn't have startled you couldn't have startled they couldn't have startled
V-ing perfect
I couldn't have been startling you couldn't have been startling he couldn't have been startling we couldn't have been startling you couldn't have been startling they couldn't 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
couldn't I startle? couldn't you startle? couldn't he startle? couldn't we startle? couldn't you startle? couldn't they startle?
V-ing form
couldn't I be startling? couldn't you be startling? couldn't he be startling? couldn't we be startling? couldn't you be startling? couldn't they be startling?
Perfect
couldn't I have startled? couldn't you have startled? couldn't he have startled? couldn't we have startled? couldn't you have startled? couldn't they have startled?
V-ing perfect
couldn't I have been startling? couldn't you have been startling? couldn't he have been startling? couldn't we have been startling? couldn't you have been startling? couldn't they have been startling?