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