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 couldn't participate you couldn't participate he couldn't participate we couldn't participate you couldn't participate they couldn't participate
V-ing form
I couldn't be participating you couldn't be participating he couldn't be participating we couldn't be participating you couldn't be participating they couldn't be participating
Perfect
I couldn't have participated you couldn't have participated he couldn't have participated we couldn't have participated you couldn't have participated they couldn't have participated
V-ing perfect
I couldn't have been participating you couldn't have been participating he couldn't have been participating we couldn't have been participating you couldn't have been participating they couldn't 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
couldn't I participate? couldn't you participate? couldn't he participate? couldn't we participate? couldn't you participate? couldn't they participate?
V-ing form
couldn't I be participating? couldn't you be participating? couldn't he be participating? couldn't we be participating? couldn't you be participating? couldn't they be participating?
Perfect
couldn't I have participated? couldn't you have participated? couldn't he have participated? couldn't we have participated? couldn't you have participated? couldn't they have participated?
V-ing perfect
couldn't I have been participating? couldn't you have been participating? couldn't he have been participating? couldn't we have been participating? couldn't you have been participating? couldn't they have been participating?