English verb conjugation
CAN SUM

Regular verb: sum - summed - summed

Affirmation

Simple form	V-ing form
I can sum you can sum she can sum we can sum you can sum they can sum	I can be summing you can be summing she can be summing we can be summing you can be summing they can be summing
Perfect	V-ing perfect
I can have summed you can have summed she can have summed we can have summed you can have summed they can have summed	I can have been summing you can have been summing she can have been summing we can have been summing you can have been summing they can have been summing

Negation

Simple form	V-ing form
I cannot sum you cannot sum she cannot sum we cannot sum you cannot sum they cannot sum	I cannot be summing you cannot be summing she cannot be summing we cannot be summing you cannot be summing they cannot be summing
Perfect	V-ing perfect
I cannot have summed you cannot have summed she cannot have summed we cannot have summed you cannot have summed they cannot have summed	I cannot have been summing you cannot have been summing she cannot have been summing we cannot have been summing you cannot have been summing they cannot have been summing

Interrogative form

Simple form	V-ing form
can I sum? can you sum? can she sum? can we sum? can you sum? can they sum?	can I be summing? can you be summing? can she be summing? can we be summing? can you be summing? can they be summing?
Perfect	V-ing perfect
can I have summed? can you have summed? can she have summed? can we have summed? can you have summed? can they have summed?	can I have been summing? can you have been summing? can she have been summing? can we have been summing? can you have been summing? can they have been summing?

Interro-negative form

Simple form	V-ing form
can I not sum? can you not sum? can she not sum? can we not sum? can you not sum? can they not sum?	can I not be summing? can you not be summing? can she not be summing? can we not be summing? can you not be summing? can they not be summing?
Perfect	V-ing perfect
can I not have summed? can you not have summed? can she not have summed? can we not have summed? can you not have summed? can they not have summed?	can I not have been summing? can you not have been summing? can she not have been summing? can we not have been summing? can you not have been summing? can they not have been summing?