I can sum you can sum he can sum we can sum you can sum they can sum
V-ing form
I can be summing you can be summing he can be summing we can be summing you can be summing they can be summing
Perfect
I can have summed you can have summed he can have summed we can have summed you can have summed they can have summed
V-ing perfect
I can have been summing you can have been summing he can have been summing we can have been summing you can have been summing they can have been summing
Negation
Simple form
I cannot sum you cannot sum he cannot sum we cannot sum you cannot sum they cannot sum
V-ing form
I cannot be summing you cannot be summing he cannot be summing we cannot be summing you cannot be summing they cannot be summing
Perfect
I cannot have summed you cannot have summed he cannot have summed we cannot have summed you cannot have summed they cannot have summed
V-ing perfect
I cannot have been summing you cannot have been summing he cannot have been summing we cannot have been summing you cannot have been summing they cannot have been summing
Interrogative form
Simple form
can I sum? can you sum? can he sum? can we sum? can you sum? can they sum?
V-ing form
can I be summing? can you be summing? can he be summing? can we be summing? can you be summing? can they be summing?
Perfect
can I have summed? can you have summed? can he have summed? can we have summed? can you have summed? can they have summed?
V-ing perfect
can I have been summing? can you have been summing? can he have been summing? can we have been summing? can you have been summing? can they have been summing?
Interro-negative form
Simple form
can I not sum? can you not sum? can he not sum? can we not sum? can you not sum? can they not sum?
V-ing form
can I not be summing? can you not be summing? can he not be summing? can we not be summing? can you not be summing? can they not be summing?
Perfect
can I not have summed? can you not have summed? can he not have summed? can we not have summed? can you not have summed? can they not have summed?
V-ing perfect
can I not have been summing? can you not have been summing? can he not have been summing? can we not have been summing? can you not have been summing? can they not have been summing?