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