I could participate you could participate he could participate we could participate you could participate they could participate
V-ing form
I could be participating you could be participating he could be participating we could be participating you could be participating they could be participating
Perfect
I could have participated you could have participated he could have participated we could have participated you could have participated they could have participated
V-ing perfect
I could have been participating you could have been participating he could have been participating we could have been participating you could have been participating they could have been participating
Negation
Simple form
I could not participate you could not participate he could not participate we could not participate you could not participate they could not participate
V-ing form
I could not be participating you could not be participating he could not be participating we could not be participating you could not be participating they could not be participating
Perfect
I could not have participated you could not have participated he could not have participated we could not have participated you could not have participated they could not have participated
V-ing perfect
I could not have been participating you could not have been participating he could not have been participating we could not have been participating you could not have been participating they could not have been participating
Interrogative form
Simple form
could I participate? could you participate? could he participate? could we participate? could you participate? could they participate?
V-ing form
could I be participating? could you be participating? could he be participating? could we be participating? could you be participating? could they be participating?
Perfect
could I have participated? could you have participated? could he have participated? could we have participated? could you have participated? could they have participated?
V-ing perfect
could I have been participating? could you have been participating? could he have been participating? could we have been participating? could you have been participating? could they have been participating?
Interro-negative form
Simple form
could I not participate? could you not participate? could he not participate? could we not participate? could you not participate? could they not participate?
V-ing form
could I not be participating? could you not be participating? could he not be participating? could we not be participating? could you not be participating? could they not be participating?
Perfect
could I not have participated? could you not have participated? could he not have participated? could we not have participated? could you not have participated? could they not have participated?
V-ing perfect
could I not have been participating? could you not have been participating? could he not have been participating? could we not have been participating? could you not have been participating? could they not have been participating?