I can lengthen you can lengthen he can lengthen we can lengthen you can lengthen they can lengthen
V-ing form
I can be lengthening you can be lengthening he can be lengthening we can be lengthening you can be lengthening they can be lengthening
Perfect
I can have lengthened you can have lengthened he can have lengthened we can have lengthened you can have lengthened they can have lengthened
V-ing perfect
I can have been lengthening you can have been lengthening he can have been lengthening we can have been lengthening you can have been lengthening they can have been lengthening
Negation
Simple form
I can't lengthen you can't lengthen he can't lengthen we can't lengthen you can't lengthen they can't lengthen
V-ing form
I can't be lengthening you can't be lengthening he can't be lengthening we can't be lengthening you can't be lengthening they can't be lengthening
Perfect
I can't have lengthened you can't have lengthened he can't have lengthened we can't have lengthened you can't have lengthened they can't have lengthened
V-ing perfect
I can't have been lengthening you can't have been lengthening he can't have been lengthening we can't have been lengthening you can't have been lengthening they can't have been lengthening
Interrogative form
Simple form
can I lengthen? can you lengthen? can he lengthen? can we lengthen? can you lengthen? can they lengthen?
V-ing form
can I be lengthening? can you be lengthening? can he be lengthening? can we be lengthening? can you be lengthening? can they be lengthening?
Perfect
can I have lengthened? can you have lengthened? can he have lengthened? can we have lengthened? can you have lengthened? can they have lengthened?
V-ing perfect
can I have been lengthening? can you have been lengthening? can he have been lengthening? can we have been lengthening? can you have been lengthening? can they have been lengthening?
Interro-negative form
Simple form
can't I lengthen? can't you lengthen? can't he lengthen? can't we lengthen? can't you lengthen? can't they lengthen?
V-ing form
can't I be lengthening? can't you be lengthening? can't he be lengthening? can't we be lengthening? can't you be lengthening? can't they be lengthening?
Perfect
can't I have lengthened? can't you have lengthened? can't he have lengthened? can't we have lengthened? can't you have lengthened? can't they have lengthened?
V-ing perfect
can't I have been lengthening? can't you have been lengthening? can't he have been lengthening? can't we have been lengthening? can't you have been lengthening? can't they have been lengthening?