can sum
Regular verb: sum - summed- summed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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	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 	Perfect 	V-ing perfect 	
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	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 	Perfect 	V-ing perfect 	
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? 	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 	Perfect 	V-ing perfect 	
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? 	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?