I can weaken you can weaken he can weaken we can weaken you can weaken they can weaken
V-ing form
I can be weakening you can be weakening he can be weakening we can be weakening you can be weakening they can be weakening
Perfect
I can have weakened you can have weakened he can have weakened we can have weakened you can have weakened they can have weakened
V-ing perfect
I can have been weakening you can have been weakening he can have been weakening we can have been weakening you can have been weakening they can have been weakening
Negation
Simple form
I can't weaken you can't weaken he can't weaken we can't weaken you can't weaken they can't weaken
V-ing form
I can't be weakening you can't be weakening he can't be weakening we can't be weakening you can't be weakening they can't be weakening
Perfect
I can't have weakened you can't have weakened he can't have weakened we can't have weakened you can't have weakened they can't have weakened
V-ing perfect
I can't have been weakening you can't have been weakening he can't have been weakening we can't have been weakening you can't have been weakening they can't have been weakening
Interrogative form
Simple form
can I weaken? can you weaken? can he weaken? can we weaken? can you weaken? can they weaken?
V-ing form
can I be weakening? can you be weakening? can he be weakening? can we be weakening? can you be weakening? can they be weakening?
Perfect
can I have weakened? can you have weakened? can he have weakened? can we have weakened? can you have weakened? can they have weakened?
V-ing perfect
can I have been weakening? can you have been weakening? can he have been weakening? can we have been weakening? can you have been weakening? can they have been weakening?
Interro-negative form
Simple form
can't I weaken? can't you weaken? can't he weaken? can't we weaken? can't you weaken? can't they weaken?
V-ing form
can't I be weakening? can't you be weakening? can't he be weakening? can't we be weakening? can't you be weakening? can't they be weakening?
Perfect
can't I have weakened? can't you have weakened? can't he have weakened? can't we have weakened? can't you have weakened? can't they have weakened?
V-ing perfect
can't I have been weakening? can't you have been weakening? can't he have been weakening? can't we have been weakening? can't you have been weakening? can't they have been weakening?