
Verbe régulier : happen -  happened - happened
Traduction française : arriver - se passer 
| Forme simple | Forme en V-ing | 
| - - it could happen - - - | - - it could be happening - - - | 
| Perfect | Perfect en V-ing | 
| - - it could have happened - - - | - - it could have been happening - - - | 
| Forme simple | Forme en V-ing | 
| - - it couldn't happen - - - | - - it couldn't be happening - - - | 
| Perfect | Perfect en V-ing | 
| - - it couldn't have happened - - - | - - it couldn't have been happening - - - | 
| Forme simple | Forme en V-ing | 
| - - could it happen? - - - | - - could it be happening? - - - | 
| Perfect | Perfect en V-ing | 
| - - could it have happened? - - - | - - could it have been happening? - - - | 
| Forme simple | Forme en V-ing | 
| - - couldn't it happen? - - - | - - couldn't it be happening? - - - | 
| Perfect | Perfect en V-ing | 
| - - couldn't it have happened? - - - | - - couldn't it have been happening? - - - |