I could travail you could travail he could travail we could travail you could travail they could travail
V-ing form
I could be travailing you could be travailing he could be travailing we could be travailing you could be travailing they could be travailing
Perfect
I could have travailed you could have travailed he 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 he could have been travailing we could have been travailing you could have been travailing they could have been travailing
Negation
Simple form
I could not travail you could not travail he could not travail we could not travail you could not travail they could not travail
V-ing form
I could not be travailing you could not be travailing he could not be travailing we could not be travailing you could not be travailing they could not be travailing
Perfect
I could not have travailed you could not have travailed he could not have travailed we could not have travailed you could not have travailed they could not have travailed
V-ing perfect
I could not have been travailing you could not have been travailing he could not have been travailing we could not have been travailing you could not have been travailing they could not have been travailing
Interrogative form
Simple form
could I travail? could you travail? could he travail? could we travail? could you travail? could they travail?
V-ing form
could I be travailing? could you be travailing? could he be travailing? could we be travailing? could you be travailing? could they be travailing?
Perfect
could I have travailed? could you have travailed? could he 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 he have been travailing? could we have been travailing? could you have been travailing? could they have been travailing?
Interro-negative form
Simple form
could I not travail? could you not travail? could he not travail? could we not travail? could you not travail? could they not travail?
V-ing form
could I not be travailing? could you not be travailing? could he not be travailing? could we not be travailing? could you not be travailing? could they not be travailing?
Perfect
could I not have travailed? could you not have travailed? could he not have travailed? could we not have travailed? could you not have travailed? could they not have travailed?
V-ing perfect
could I not have been travailing? could you not have been travailing? could he not have been travailing? could we not have been travailing? could you not have been travailing? could they not have been travailing?