I can certify you can certify he can certify we can certify you can certify they can certify
V-ing form
I can be certifying you can be certifying he can be certifying we can be certifying you can be certifying they can be certifying
Perfect
I can have certified you can have certified he can have certified we can have certified you can have certified they can have certified
V-ing perfect
I can have been certifying you can have been certifying he can have been certifying we can have been certifying you can have been certifying they can have been certifying
Negation
Simple form
I can't certify you can't certify he can't certify we can't certify you can't certify they can't certify
V-ing form
I can't be certifying you can't be certifying he can't be certifying we can't be certifying you can't be certifying they can't be certifying
Perfect
I can't have certified you can't have certified he can't have certified we can't have certified you can't have certified they can't have certified
V-ing perfect
I can't have been certifying you can't have been certifying he can't have been certifying we can't have been certifying you can't have been certifying they can't have been certifying
Interrogative form
Simple form
can I certify? can you certify? can he certify? can we certify? can you certify? can they certify?
V-ing form
can I be certifying? can you be certifying? can he be certifying? can we be certifying? can you be certifying? can they be certifying?
Perfect
can I have certified? can you have certified? can he have certified? can we have certified? can you have certified? can they have certified?
V-ing perfect
can I have been certifying? can you have been certifying? can he have been certifying? can we have been certifying? can you have been certifying? can they have been certifying?
Interro-negative form
Simple form
can't I certify? can't you certify? can't he certify? can't we certify? can't you certify? can't they certify?
V-ing form
can't I be certifying? can't you be certifying? can't he be certifying? can't we be certifying? can't you be certifying? can't they be certifying?
Perfect
can't I have certified? can't you have certified? can't he have certified? can't we have certified? can't you have certified? can't they have certified?
V-ing perfect
can't I have been certifying? can't you have been certifying? can't he have been certifying? can't we have been certifying? can't you have been certifying? can't they have been certifying?