I could crumble you could crumble he could crumble we could crumble you could crumble they could crumble
V-ing form
I could be crumbling you could be crumbling he could be crumbling we could be crumbling you could be crumbling they could be crumbling
Perfect
I could have crumbled you could have crumbled he could have crumbled we could have crumbled you could have crumbled they could have crumbled
V-ing perfect
I could have been crumbling you could have been crumbling he could have been crumbling we could have been crumbling you could have been crumbling they could have been crumbling
Negation
Simple form
I could not crumble you could not crumble he could not crumble we could not crumble you could not crumble they could not crumble
V-ing form
I could not be crumbling you could not be crumbling he could not be crumbling we could not be crumbling you could not be crumbling they could not be crumbling
Perfect
I could not have crumbled you could not have crumbled he could not have crumbled we could not have crumbled you could not have crumbled they could not have crumbled
V-ing perfect
I could not have been crumbling you could not have been crumbling he could not have been crumbling we could not have been crumbling you could not have been crumbling they could not have been crumbling
Interrogative form
Simple form
could I crumble? could you crumble? could he crumble? could we crumble? could you crumble? could they crumble?
V-ing form
could I be crumbling? could you be crumbling? could he be crumbling? could we be crumbling? could you be crumbling? could they be crumbling?
Perfect
could I have crumbled? could you have crumbled? could he have crumbled? could we have crumbled? could you have crumbled? could they have crumbled?
V-ing perfect
could I have been crumbling? could you have been crumbling? could he have been crumbling? could we have been crumbling? could you have been crumbling? could they have been crumbling?
Interro-negative form
Simple form
could I not crumble? could you not crumble? could he not crumble? could we not crumble? could you not crumble? could they not crumble?
V-ing form
could I not be crumbling? could you not be crumbling? could he not be crumbling? could we not be crumbling? could you not be crumbling? could they not be crumbling?
Perfect
could I not have crumbled? could you not have crumbled? could he not have crumbled? could we not have crumbled? could you not have crumbled? could they not have crumbled?
V-ing perfect
could I not have been crumbling? could you not have been crumbling? could he not have been crumbling? could we not have been crumbling? could you not have been crumbling? could they not have been crumbling?