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