English verb conjugation
COULD GRUB

Regular verb: grub - grubbed - grubbed

Affirmation

Simple form	V-ing form
I could grub you could grub he could grub we could grub you could grub they could grub	I could be grubbing you could be grubbing he could be grubbing we could be grubbing you could be grubbing they could be grubbing
Perfect	V-ing perfect
I could have grubbed you could have grubbed he could have grubbed we could have grubbed you could have grubbed they could have grubbed	I could have been grubbing you could have been grubbing he could have been grubbing we could have been grubbing you could have been grubbing they could have been grubbing

Negation

Simple form	V-ing form
I could not grub you could not grub he could not grub we could not grub you could not grub they could not grub	I could not be grubbing you could not be grubbing he could not be grubbing we could not be grubbing you could not be grubbing they could not be grubbing
Perfect	V-ing perfect
I could not have grubbed you could not have grubbed he could not have grubbed we could not have grubbed you could not have grubbed they could not have grubbed	I could not have been grubbing you could not have been grubbing he could not have been grubbing we could not have been grubbing you could not have been grubbing they could not have been grubbing

Interrogative form

Simple form	V-ing form
could I grub? could you grub? could he grub? could we grub? could you grub? could they grub?	could I be grubbing? could you be grubbing? could he be grubbing? could we be grubbing? could you be grubbing? could they be grubbing?
Perfect	V-ing perfect
could I have grubbed? could you have grubbed? could he have grubbed? could we have grubbed? could you have grubbed? could they have grubbed?	could I have been grubbing? could you have been grubbing? could he have been grubbing? could we have been grubbing? could you have been grubbing? could they have been grubbing?

Interro-negative form

Simple form	V-ing form
could I not grub? could you not grub? could he not grub? could we not grub? could you not grub? could they not grub?	could I not be grubbing? could you not be grubbing? could he not be grubbing? could we not be grubbing? could you not be grubbing? could they not be grubbing?
Perfect	V-ing perfect
could I not have grubbed? could you not have grubbed? could he not have grubbed? could we not have grubbed? could you not have grubbed? could they not have grubbed?	could I not have been grubbing? could you not have been grubbing? could he not have been grubbing? could we not have been grubbing? could you not have been grubbing? could they not have been grubbing?