I can ski you can ski he can ski we can ski you can ski they can ski
V-ing form
I can be skiing you can be skiing he can be skiing we can be skiing you can be skiing they can be skiing
Perfect
I can have skied you can have skied he can have skied we can have skied you can have skied they can have skied
V-ing perfect
I can have been skiing you can have been skiing he can have been skiing we can have been skiing you can have been skiing they can have been skiing
Negation
Simple form
I can't ski you can't ski he can't ski we can't ski you can't ski they can't ski
V-ing form
I can't be skiing you can't be skiing he can't be skiing we can't be skiing you can't be skiing they can't be skiing
Perfect
I can't have skied you can't have skied he can't have skied we can't have skied you can't have skied they can't have skied
V-ing perfect
I can't have been skiing you can't have been skiing he can't have been skiing we can't have been skiing you can't have been skiing they can't have been skiing
Interrogative form
Simple form
can I ski? can you ski? can he ski? can we ski? can you ski? can they ski?
V-ing form
can I be skiing? can you be skiing? can he be skiing? can we be skiing? can you be skiing? can they be skiing?
Perfect
can I have skied? can you have skied? can he have skied? can we have skied? can you have skied? can they have skied?
V-ing perfect
can I have been skiing? can you have been skiing? can he have been skiing? can we have been skiing? can you have been skiing? can they have been skiing?
Interro-negative form
Simple form
can't I ski? can't you ski? can't he ski? can't we ski? can't you ski? can't they ski?
V-ing form
can't I be skiing? can't you be skiing? can't he be skiing? can't we be skiing? can't you be skiing? can't they be skiing?
Perfect
can't I have skied? can't you have skied? can't he have skied? can't we have skied? can't you have skied? can't they have skied?
V-ing perfect
can't I have been skiing? can't you have been skiing? can't he have been skiing? can't we have been skiing? can't you have been skiing? can't they have been skiing?