English verb conjugation
COULD SUM

Regular verb: sum - summed - summed

Affirmation

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

Negation

Simple form	V-ing form
I couldn't sum you couldn't sum he couldn't sum we couldn't sum you couldn't sum they couldn't sum	I couldn't be summing you couldn't be summing he couldn't be summing we couldn't be summing you couldn't be summing they couldn't be summing
Perfect	V-ing perfect
I couldn't have summed you couldn't have summed he couldn't have summed we couldn't have summed you couldn't have summed they couldn't have summed	I couldn't have been summing you couldn't have been summing he couldn't have been summing we couldn't have been summing you couldn't have been summing they couldn't have been summing

Interrogative form

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

Interro-negative form

Simple form	V-ing form
couldn't I sum? couldn't you sum? couldn't he sum? couldn't we sum? couldn't you sum? couldn't they sum?	couldn't I be summing? couldn't you be summing? couldn't he be summing? couldn't we be summing? couldn't you be summing? couldn't they be summing?
Perfect	V-ing perfect
couldn't I have summed? couldn't you have summed? couldn't he have summed? couldn't we have summed? couldn't you have summed? couldn't they have summed?	couldn't I have been summing? couldn't you have been summing? couldn't he have been summing? couldn't we have been summing? couldn't you have been summing? couldn't they have been summing?