I could sour you could sour he could sour we could sour you could sour they could sour
V-ing form
I could be souring you could be souring he could be souring we could be souring you could be souring they could be souring
Perfect
I could have soured you could have soured he could have soured we could have soured you could have soured they could have soured
V-ing perfect
I could have been souring you could have been souring he could have been souring we could have been souring you could have been souring they could have been souring
Negation
Simple form
I could not sour you could not sour he could not sour we could not sour you could not sour they could not sour
V-ing form
I could not be souring you could not be souring he could not be souring we could not be souring you could not be souring they could not be souring
Perfect
I could not have soured you could not have soured he could not have soured we could not have soured you could not have soured they could not have soured
V-ing perfect
I could not have been souring you could not have been souring he could not have been souring we could not have been souring you could not have been souring they could not have been souring
Interrogative form
Simple form
could I sour? could you sour? could he sour? could we sour? could you sour? could they sour?
V-ing form
could I be souring? could you be souring? could he be souring? could we be souring? could you be souring? could they be souring?
Perfect
could I have soured? could you have soured? could he have soured? could we have soured? could you have soured? could they have soured?
V-ing perfect
could I have been souring? could you have been souring? could he have been souring? could we have been souring? could you have been souring? could they have been souring?
Interro-negative form
Simple form
could I not sour? could you not sour? could he not sour? could we not sour? could you not sour? could they not sour?
V-ing form
could I not be souring? could you not be souring? could he not be souring? could we not be souring? could you not be souring? could they not be souring?
Perfect
could I not have soured? could you not have soured? could he not have soured? could we not have soured? could you not have soured? could they not have soured?
V-ing perfect
could I not have been souring? could you not have been souring? could he not have been souring? could we not have been souring? could you not have been souring? could they not have been souring?