I could fishtail you could fishtail he could fishtail we could fishtail you could fishtail they could fishtail
V-ing form
I could be fishtailing you could be fishtailing he could be fishtailing we could be fishtailing you could be fishtailing they could be fishtailing
Perfect
I could have fishtailed you could have fishtailed he could have fishtailed we could have fishtailed you could have fishtailed they could have fishtailed
V-ing perfect
I could have been fishtailing you could have been fishtailing he could have been fishtailing we could have been fishtailing you could have been fishtailing they could have been fishtailing
Negation
Simple form
I could not fishtail you could not fishtail he could not fishtail we could not fishtail you could not fishtail they could not fishtail
V-ing form
I could not be fishtailing you could not be fishtailing he could not be fishtailing we could not be fishtailing you could not be fishtailing they could not be fishtailing
Perfect
I could not have fishtailed you could not have fishtailed he could not have fishtailed we could not have fishtailed you could not have fishtailed they could not have fishtailed
V-ing perfect
I could not have been fishtailing you could not have been fishtailing he could not have been fishtailing we could not have been fishtailing you could not have been fishtailing they could not have been fishtailing
Interrogative form
Simple form
could I fishtail? could you fishtail? could he fishtail? could we fishtail? could you fishtail? could they fishtail?
V-ing form
could I be fishtailing? could you be fishtailing? could he be fishtailing? could we be fishtailing? could you be fishtailing? could they be fishtailing?
Perfect
could I have fishtailed? could you have fishtailed? could he have fishtailed? could we have fishtailed? could you have fishtailed? could they have fishtailed?
V-ing perfect
could I have been fishtailing? could you have been fishtailing? could he have been fishtailing? could we have been fishtailing? could you have been fishtailing? could they have been fishtailing?
Interro-negative form
Simple form
could I not fishtail? could you not fishtail? could he not fishtail? could we not fishtail? could you not fishtail? could they not fishtail?
V-ing form
could I not be fishtailing? could you not be fishtailing? could he not be fishtailing? could we not be fishtailing? could you not be fishtailing? could they not be fishtailing?
Perfect
could I not have fishtailed? could you not have fishtailed? could he not have fishtailed? could we not have fishtailed? could you not have fishtailed? could they not have fishtailed?
V-ing perfect
could I not have been fishtailing? could you not have been fishtailing? could he not have been fishtailing? could we not have been fishtailing? could you not have been fishtailing? could they not have been fishtailing?