I could grab you could grab he could grab we could grab you could grab they could grab
V-ing form
I could be grabbing you could be grabbing he could be grabbing we could be grabbing you could be grabbing they could be grabbing
Perfect
I could have grabbed you could have grabbed he could have grabbed we could have grabbed you could have grabbed they could have grabbed
V-ing perfect
I could have been grabbing you could have been grabbing he could have been grabbing we could have been grabbing you could have been grabbing they could have been grabbing
Negation
Simple form
I could not grab you could not grab he could not grab we could not grab you could not grab they could not grab
V-ing form
I could not be grabbing you could not be grabbing he could not be grabbing we could not be grabbing you could not be grabbing they could not be grabbing
Perfect
I could not have grabbed you could not have grabbed he could not have grabbed we could not have grabbed you could not have grabbed they could not have grabbed
V-ing perfect
I could not have been grabbing you could not have been grabbing he could not have been grabbing we could not have been grabbing you could not have been grabbing they could not have been grabbing
Interrogative form
Simple form
could I grab? could you grab? could he grab? could we grab? could you grab? could they grab?
V-ing form
could I be grabbing? could you be grabbing? could he be grabbing? could we be grabbing? could you be grabbing? could they be grabbing?
Perfect
could I have grabbed? could you have grabbed? could he have grabbed? could we have grabbed? could you have grabbed? could they have grabbed?
V-ing perfect
could I have been grabbing? could you have been grabbing? could he have been grabbing? could we have been grabbing? could you have been grabbing? could they have been grabbing?
Interro-negative form
Simple form
could I not grab? could you not grab? could he not grab? could we not grab? could you not grab? could they not grab?
V-ing form
could I not be grabbing? could you not be grabbing? could he not be grabbing? could we not be grabbing? could you not be grabbing? could they not be grabbing?
Perfect
could I not have grabbed? could you not have grabbed? could he not have grabbed? could we not have grabbed? could you not have grabbed? could they not have grabbed?
V-ing perfect
could I not have been grabbing? could you not have been grabbing? could he not have been grabbing? could we not have been grabbing? could you not have been grabbing? could they not have been grabbing?