I could grab you could grab she could grab we could grab you could grab they could grab
V-ing form
I could be grabbing you could be grabbing she could be grabbing we could be grabbing you could be grabbing they could be grabbing
Perfect
I could have grabbed you could have grabbed she 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 she could have been grabbing we could have been grabbing you could have been grabbing they could have been grabbing
Negation
Simple form
I couldn't grab you couldn't grab she couldn't grab we couldn't grab you couldn't grab they couldn't grab
V-ing form
I couldn't be grabbing you couldn't be grabbing she couldn't be grabbing we couldn't be grabbing you couldn't be grabbing they couldn't be grabbing
Perfect
I couldn't have grabbed you couldn't have grabbed she couldn't have grabbed we couldn't have grabbed you couldn't have grabbed they couldn't have grabbed
V-ing perfect
I couldn't have been grabbing you couldn't have been grabbing she couldn't have been grabbing we couldn't have been grabbing you couldn't have been grabbing they couldn't have been grabbing
Interrogative form
Simple form
could I grab? could you grab? could she grab? could we grab? could you grab? could they grab?
V-ing form
could I be grabbing? could you be grabbing? could she be grabbing? could we be grabbing? could you be grabbing? could they be grabbing?
Perfect
could I have grabbed? could you have grabbed? could she 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 she have been grabbing? could we have been grabbing? could you have been grabbing? could they have been grabbing?
Interro-negative form
Simple form
couldn't I grab? couldn't you grab? couldn't she grab? couldn't we grab? couldn't you grab? couldn't they grab?
V-ing form
couldn't I be grabbing? couldn't you be grabbing? couldn't she be grabbing? couldn't we be grabbing? couldn't you be grabbing? couldn't they be grabbing?
Perfect
couldn't I have grabbed? couldn't you have grabbed? couldn't she have grabbed? couldn't we have grabbed? couldn't you have grabbed? couldn't they have grabbed?
V-ing perfect
couldn't I have been grabbing? couldn't you have been grabbing? couldn't she have been grabbing? couldn't we have been grabbing? couldn't you have been grabbing? couldn't they have been grabbing?