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