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