I could think you could think he could think we could think you could think they could think
V-ing form
I could be thinking you could be thinking he could be thinking we could be thinking you could be thinking they could be thinking
Perfect
I could have thought you could have thought he could have thought we could have thought you could have thought they could have thought
V-ing perfect
I could have been thinking you could have been thinking he could have been thinking we could have been thinking you could have been thinking they could have been thinking
Negation
Simple form
I could not think you could not think he could not think we could not think you could not think they could not think
V-ing form
I could not be thinking you could not be thinking he could not be thinking we could not be thinking you could not be thinking they could not be thinking
Perfect
I could not have thought you could not have thought he could not have thought we could not have thought you could not have thought they could not have thought
V-ing perfect
I could not have been thinking you could not have been thinking he could not have been thinking we could not have been thinking you could not have been thinking they could not have been thinking
Interrogative form
Simple form
could I think? could you think? could he think? could we think? could you think? could they think?
V-ing form
could I be thinking? could you be thinking? could he be thinking? could we be thinking? could you be thinking? could they be thinking?
Perfect
could I have thought? could you have thought? could he have thought? could we have thought? could you have thought? could they have thought?
V-ing perfect
could I have been thinking? could you have been thinking? could he have been thinking? could we have been thinking? could you have been thinking? could they have been thinking?
Interro-negative form
Simple form
could I not think? could you not think? could he not think? could we not think? could you not think? could they not think?
V-ing form
could I not be thinking? could you not be thinking? could he not be thinking? could we not be thinking? could you not be thinking? could they not be thinking?
Perfect
could I not have thought? could you not have thought? could he not have thought? could we not have thought? could you not have thought? could they not have thought?
V-ing perfect
could I not have been thinking? could you not have been thinking? could he not have been thinking? could we not have been thinking? could you not have been thinking? could they not have been thinking?