I could excavate you could excavate he could excavate we could excavate you could excavate they could excavate
V-ing form
I could be excavating you could be excavating he could be excavating we could be excavating you could be excavating they could be excavating
Perfect
I could have excavated you could have excavated he could have excavated we could have excavated you could have excavated they could have excavated
V-ing perfect
I could have been excavating you could have been excavating he could have been excavating we could have been excavating you could have been excavating they could have been excavating
Negation
Simple form
I could not excavate you could not excavate he could not excavate we could not excavate you could not excavate they could not excavate
V-ing form
I could not be excavating you could not be excavating he could not be excavating we could not be excavating you could not be excavating they could not be excavating
Perfect
I could not have excavated you could not have excavated he could not have excavated we could not have excavated you could not have excavated they could not have excavated
V-ing perfect
I could not have been excavating you could not have been excavating he could not have been excavating we could not have been excavating you could not have been excavating they could not have been excavating
Interrogative form
Simple form
could I excavate? could you excavate? could he excavate? could we excavate? could you excavate? could they excavate?
V-ing form
could I be excavating? could you be excavating? could he be excavating? could we be excavating? could you be excavating? could they be excavating?
Perfect
could I have excavated? could you have excavated? could he have excavated? could we have excavated? could you have excavated? could they have excavated?
V-ing perfect
could I have been excavating? could you have been excavating? could he have been excavating? could we have been excavating? could you have been excavating? could they have been excavating?
Interro-negative form
Simple form
could I not excavate? could you not excavate? could he not excavate? could we not excavate? could you not excavate? could they not excavate?
V-ing form
could I not be excavating? could you not be excavating? could he not be excavating? could we not be excavating? could you not be excavating? could they not be excavating?
Perfect
could I not have excavated? could you not have excavated? could he not have excavated? could we not have excavated? could you not have excavated? could they not have excavated?
V-ing perfect
could I not have been excavating? could you not have been excavating? could he not have been excavating? could we not have been excavating? could you not have been excavating? could they not have been excavating?