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 couldn't grub you couldn't grub he couldn't grub we couldn't grub you couldn't grub they couldn't grub	I couldn't be grubbing you couldn't be grubbing he couldn't be grubbing we couldn't be grubbing you couldn't be grubbing they couldn't be grubbing
Perfect	V-ing perfect
I couldn't have grubbed you couldn't have grubbed he couldn't have grubbed we couldn't have grubbed you couldn't have grubbed they couldn't have grubbed	I couldn't have been grubbing you couldn't have been grubbing he couldn't have been grubbing we couldn't have been grubbing you couldn't have been grubbing they couldn't 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
couldn't I grub? couldn't you grub? couldn't he grub? couldn't we grub? couldn't you grub? couldn't they grub?	couldn't I be grubbing? couldn't you be grubbing? couldn't he be grubbing? couldn't we be grubbing? couldn't you be grubbing? couldn't they be grubbing?
Perfect	V-ing perfect
couldn't I have grubbed? couldn't you have grubbed? couldn't he have grubbed? couldn't we have grubbed? couldn't you have grubbed? couldn't they have grubbed?	couldn't I have been grubbing? couldn't you have been grubbing? couldn't he have been grubbing? couldn't we have been grubbing? couldn't you have been grubbing? couldn't they have been grubbing?