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