I could compute you could compute he could compute we could compute you could compute they could compute
V-ing form
I could be computing you could be computing he could be computing we could be computing you could be computing they could be computing
Perfect
I could have computed you could have computed he could have computed we could have computed you could have computed they could have computed
V-ing perfect
I could have been computing you could have been computing he could have been computing we could have been computing you could have been computing they could have been computing
Negation
Simple form
I couldn't compute you couldn't compute he couldn't compute we couldn't compute you couldn't compute they couldn't compute
V-ing form
I couldn't be computing you couldn't be computing he couldn't be computing we couldn't be computing you couldn't be computing they couldn't be computing
Perfect
I couldn't have computed you couldn't have computed he couldn't have computed we couldn't have computed you couldn't have computed they couldn't have computed
V-ing perfect
I couldn't have been computing you couldn't have been computing he couldn't have been computing we couldn't have been computing you couldn't have been computing they couldn't have been computing
Interrogative form
Simple form
could I compute? could you compute? could he compute? could we compute? could you compute? could they compute?
V-ing form
could I be computing? could you be computing? could he be computing? could we be computing? could you be computing? could they be computing?
Perfect
could I have computed? could you have computed? could he have computed? could we have computed? could you have computed? could they have computed?
V-ing perfect
could I have been computing? could you have been computing? could he have been computing? could we have been computing? could you have been computing? could they have been computing?
Interro-negative form
Simple form
couldn't I compute? couldn't you compute? couldn't he compute? couldn't we compute? couldn't you compute? couldn't they compute?
V-ing form
couldn't I be computing? couldn't you be computing? couldn't he be computing? couldn't we be computing? couldn't you be computing? couldn't they be computing?
Perfect
couldn't I have computed? couldn't you have computed? couldn't he have computed? couldn't we have computed? couldn't you have computed? couldn't they have computed?
V-ing perfect
couldn't I have been computing? couldn't you have been computing? couldn't he have been computing? couldn't we have been computing? couldn't you have been computing? couldn't they have been computing?