I can skate you can skate he can skate we can skate you can skate they can skate
V-ing form
I can be skating you can be skating he can be skating we can be skating you can be skating they can be skating
Perfect
I can have skated you can have skated he can have skated we can have skated you can have skated they can have skated
V-ing perfect
I can have been skating you can have been skating he can have been skating we can have been skating you can have been skating they can have been skating
Negation
Simple form
I cannot skate you cannot skate he cannot skate we cannot skate you cannot skate they cannot skate
V-ing form
I cannot be skating you cannot be skating he cannot be skating we cannot be skating you cannot be skating they cannot be skating
Perfect
I cannot have skated you cannot have skated he cannot have skated we cannot have skated you cannot have skated they cannot have skated
V-ing perfect
I cannot have been skating you cannot have been skating he cannot have been skating we cannot have been skating you cannot have been skating they cannot have been skating
Interrogative form
Simple form
can I skate? can you skate? can he skate? can we skate? can you skate? can they skate?
V-ing form
can I be skating? can you be skating? can he be skating? can we be skating? can you be skating? can they be skating?
Perfect
can I have skated? can you have skated? can he have skated? can we have skated? can you have skated? can they have skated?
V-ing perfect
can I have been skating? can you have been skating? can he have been skating? can we have been skating? can you have been skating? can they have been skating?
Interro-negative form
Simple form
can I not skate? can you not skate? can he not skate? can we not skate? can you not skate? can they not skate?
V-ing form
can I not be skating? can you not be skating? can he not be skating? can we not be skating? can you not be skating? can they not be skating?
Perfect
can I not have skated? can you not have skated? can he not have skated? can we not have skated? can you not have skated? can they not have skated?
V-ing perfect
can I not have been skating? can you not have been skating? can he not have been skating? can we not have been skating? can you not have been skating? can they not have been skating?