I could whistle you could whistle she could whistle we could whistle you could whistle they could whistle
V-ing form
I could be whistling you could be whistling she could be whistling we could be whistling you could be whistling they could be whistling
Perfect
I could have whistled you could have whistled she could have whistled we could have whistled you could have whistled they could have whistled
V-ing perfect
I could have been whistling you could have been whistling she could have been whistling we could have been whistling you could have been whistling they could have been whistling
Negation
Simple form
I couldn't whistle you couldn't whistle she couldn't whistle we couldn't whistle you couldn't whistle they couldn't whistle
V-ing form
I couldn't be whistling you couldn't be whistling she couldn't be whistling we couldn't be whistling you couldn't be whistling they couldn't be whistling
Perfect
I couldn't have whistled you couldn't have whistled she couldn't have whistled we couldn't have whistled you couldn't have whistled they couldn't have whistled
V-ing perfect
I couldn't have been whistling you couldn't have been whistling she couldn't have been whistling we couldn't have been whistling you couldn't have been whistling they couldn't have been whistling
Interrogative form
Simple form
could I whistle? could you whistle? could she whistle? could we whistle? could you whistle? could they whistle?
V-ing form
could I be whistling? could you be whistling? could she be whistling? could we be whistling? could you be whistling? could they be whistling?
Perfect
could I have whistled? could you have whistled? could she have whistled? could we have whistled? could you have whistled? could they have whistled?
V-ing perfect
could I have been whistling? could you have been whistling? could she have been whistling? could we have been whistling? could you have been whistling? could they have been whistling?
Interro-negative form
Simple form
couldn't I whistle? couldn't you whistle? couldn't she whistle? couldn't we whistle? couldn't you whistle? couldn't they whistle?
V-ing form
couldn't I be whistling? couldn't you be whistling? couldn't she be whistling? couldn't we be whistling? couldn't you be whistling? couldn't they be whistling?
Perfect
couldn't I have whistled? couldn't you have whistled? couldn't she have whistled? couldn't we have whistled? couldn't you have whistled? couldn't they have whistled?
V-ing perfect
couldn't I have been whistling? couldn't you have been whistling? couldn't she have been whistling? couldn't we have been whistling? couldn't you have been whistling? couldn't they have been whistling?