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 couldn't think you couldn't think he couldn't think we couldn't think you couldn't think they couldn't think
V-ing form
I couldn't be thinking you couldn't be thinking he couldn't be thinking we couldn't be thinking you couldn't be thinking they couldn't be thinking
Perfect
I couldn't have thought you couldn't have thought he couldn't have thought we couldn't have thought you couldn't have thought they couldn't have thought
V-ing perfect
I couldn't have been thinking you couldn't have been thinking he couldn't have been thinking we couldn't have been thinking you couldn't have been thinking they couldn't 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
couldn't I think? couldn't you think? couldn't he think? couldn't we think? couldn't you think? couldn't they think?
V-ing form
couldn't I be thinking? couldn't you be thinking? couldn't he be thinking? couldn't we be thinking? couldn't you be thinking? couldn't they be thinking?
Perfect
couldn't I have thought? couldn't you have thought? couldn't he have thought? couldn't we have thought? couldn't you have thought? couldn't they have thought?
V-ing perfect
couldn't I have been thinking? couldn't you have been thinking? couldn't he have been thinking? couldn't we have been thinking? couldn't you have been thinking? couldn't they have been thinking?