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