I could substitute you could substitute he could substitute we could substitute you could substitute they could substitute
V-ing form
I could be substituting you could be substituting he could be substituting we could be substituting you could be substituting they could be substituting
Perfect
I could have substituted you could have substituted he could have substituted we could have substituted you could have substituted they could have substituted
V-ing perfect
I could have been substituting you could have been substituting he could have been substituting we could have been substituting you could have been substituting they could have been substituting
Negation
Simple form
I could not substitute you could not substitute he could not substitute we could not substitute you could not substitute they could not substitute
V-ing form
I could not be substituting you could not be substituting he could not be substituting we could not be substituting you could not be substituting they could not be substituting
Perfect
I could not have substituted you could not have substituted he could not have substituted we could not have substituted you could not have substituted they could not have substituted
V-ing perfect
I could not have been substituting you could not have been substituting he could not have been substituting we could not have been substituting you could not have been substituting they could not have been substituting
Interrogative form
Simple form
could I substitute? could you substitute? could he substitute? could we substitute? could you substitute? could they substitute?
V-ing form
could I be substituting? could you be substituting? could he be substituting? could we be substituting? could you be substituting? could they be substituting?
Perfect
could I have substituted? could you have substituted? could he have substituted? could we have substituted? could you have substituted? could they have substituted?
V-ing perfect
could I have been substituting? could you have been substituting? could he have been substituting? could we have been substituting? could you have been substituting? could they have been substituting?
Interro-negative form
Simple form
could I not substitute? could you not substitute? could he not substitute? could we not substitute? could you not substitute? could they not substitute?
V-ing form
could I not be substituting? could you not be substituting? could he not be substituting? could we not be substituting? could you not be substituting? could they not be substituting?
Perfect
could I not have substituted? could you not have substituted? could he not have substituted? could we not have substituted? could you not have substituted? could they not have substituted?
V-ing perfect
could I not have been substituting? could you not have been substituting? could he not have been substituting? could we not have been substituting? could you not have been substituting? could they not have been substituting?