I could grind you could grind he could grind we could grind you could grind they could grind
V-ing form
I could be grinding you could be grinding he could be grinding we could be grinding you could be grinding they could be grinding
Perfect
I could have ground you could have ground he could have ground we could have ground you could have ground they could have ground
V-ing perfect
I could have been grinding you could have been grinding he could have been grinding we could have been grinding you could have been grinding they could have been grinding
Negation
Simple form
I couldn't grind you couldn't grind he couldn't grind we couldn't grind you couldn't grind they couldn't grind
V-ing form
I couldn't be grinding you couldn't be grinding he couldn't be grinding we couldn't be grinding you couldn't be grinding they couldn't be grinding
Perfect
I couldn't have ground you couldn't have ground he couldn't have ground we couldn't have ground you couldn't have ground they couldn't have ground
V-ing perfect
I couldn't have been grinding you couldn't have been grinding he couldn't have been grinding we couldn't have been grinding you couldn't have been grinding they couldn't have been grinding
Interrogative form
Simple form
could I grind? could you grind? could he grind? could we grind? could you grind? could they grind?
V-ing form
could I be grinding? could you be grinding? could he be grinding? could we be grinding? could you be grinding? could they be grinding?
Perfect
could I have ground? could you have ground? could he have ground? could we have ground? could you have ground? could they have ground?
V-ing perfect
could I have been grinding? could you have been grinding? could he have been grinding? could we have been grinding? could you have been grinding? could they have been grinding?
Interro-negative form
Simple form
couldn't I grind? couldn't you grind? couldn't he grind? couldn't we grind? couldn't you grind? couldn't they grind?
V-ing form
couldn't I be grinding? couldn't you be grinding? couldn't he be grinding? couldn't we be grinding? couldn't you be grinding? couldn't they be grinding?
Perfect
couldn't I have ground? couldn't you have ground? couldn't he have ground? couldn't we have ground? couldn't you have ground? couldn't they have ground?
V-ing perfect
couldn't I have been grinding? couldn't you have been grinding? couldn't he have been grinding? couldn't we have been grinding? couldn't you have been grinding? couldn't they have been grinding?