I could bob you could bob he could bob we could bob you could bob they could bob
V-ing form
I could be bobbing you could be bobbing he could be bobbing we could be bobbing you could be bobbing they could be bobbing
Perfect
I could have bobbed you could have bobbed he could have bobbed we could have bobbed you could have bobbed they could have bobbed
V-ing perfect
I could have been bobbing you could have been bobbing he could have been bobbing we could have been bobbing you could have been bobbing they could have been bobbing
Negation
Simple form
I could not bob you could not bob he could not bob we could not bob you could not bob they could not bob
V-ing form
I could not be bobbing you could not be bobbing he could not be bobbing we could not be bobbing you could not be bobbing they could not be bobbing
Perfect
I could not have bobbed you could not have bobbed he could not have bobbed we could not have bobbed you could not have bobbed they could not have bobbed
V-ing perfect
I could not have been bobbing you could not have been bobbing he could not have been bobbing we could not have been bobbing you could not have been bobbing they could not have been bobbing
Interrogative form
Simple form
could I bob? could you bob? could he bob? could we bob? could you bob? could they bob?
V-ing form
could I be bobbing? could you be bobbing? could he be bobbing? could we be bobbing? could you be bobbing? could they be bobbing?
Perfect
could I have bobbed? could you have bobbed? could he have bobbed? could we have bobbed? could you have bobbed? could they have bobbed?
V-ing perfect
could I have been bobbing? could you have been bobbing? could he have been bobbing? could we have been bobbing? could you have been bobbing? could they have been bobbing?
Interro-negative form
Simple form
could I not bob? could you not bob? could he not bob? could we not bob? could you not bob? could they not bob?
V-ing form
could I not be bobbing? could you not be bobbing? could he not be bobbing? could we not be bobbing? could you not be bobbing? could they not be bobbing?
Perfect
could I not have bobbed? could you not have bobbed? could he not have bobbed? could we not have bobbed? could you not have bobbed? could they not have bobbed?
V-ing perfect
could I not have been bobbing? could you not have been bobbing? could he not have been bobbing? could we not have been bobbing? could you not have been bobbing? could they not have been bobbing?