I could solve you could solve he could solve we could solve you could solve they could solve
V-ing form
I could be solving you could be solving he could be solving we could be solving you could be solving they could be solving
Perfect
I could have solved you could have solved he could have solved we could have solved you could have solved they could have solved
V-ing perfect
I could have been solving you could have been solving he could have been solving we could have been solving you could have been solving they could have been solving
Negation
Simple form
I could not solve you could not solve he could not solve we could not solve you could not solve they could not solve
V-ing form
I could not be solving you could not be solving he could not be solving we could not be solving you could not be solving they could not be solving
Perfect
I could not have solved you could not have solved he could not have solved we could not have solved you could not have solved they could not have solved
V-ing perfect
I could not have been solving you could not have been solving he could not have been solving we could not have been solving you could not have been solving they could not have been solving
Interrogative form
Simple form
could I solve? could you solve? could he solve? could we solve? could you solve? could they solve?
V-ing form
could I be solving? could you be solving? could he be solving? could we be solving? could you be solving? could they be solving?
Perfect
could I have solved? could you have solved? could he have solved? could we have solved? could you have solved? could they have solved?
V-ing perfect
could I have been solving? could you have been solving? could he have been solving? could we have been solving? could you have been solving? could they have been solving?
Interro-negative form
Simple form
could I not solve? could you not solve? could he not solve? could we not solve? could you not solve? could they not solve?
V-ing form
could I not be solving? could you not be solving? could he not be solving? could we not be solving? could you not be solving? could they not be solving?
Perfect
could I not have solved? could you not have solved? could he not have solved? could we not have solved? could you not have solved? could they not have solved?
V-ing perfect
could I not have been solving? could you not have been solving? could he not have been solving? could we not have been solving? could you not have been solving? could they not have been solving?