I could grade you could grade she could grade we could grade you could grade they could grade
V-ing form
I could be grading you could be grading she could be grading we could be grading you could be grading they could be grading
Perfect
I could have graded you could have graded she could have graded we could have graded you could have graded they could have graded
V-ing perfect
I could have been grading you could have been grading she could have been grading we could have been grading you could have been grading they could have been grading
Negation
Simple form
I could not grade you could not grade she could not grade we could not grade you could not grade they could not grade
V-ing form
I could not be grading you could not be grading she could not be grading we could not be grading you could not be grading they could not be grading
Perfect
I could not have graded you could not have graded she could not have graded we could not have graded you could not have graded they could not have graded
V-ing perfect
I could not have been grading you could not have been grading she could not have been grading we could not have been grading you could not have been grading they could not have been grading
Interrogative form
Simple form
could I grade? could you grade? could she grade? could we grade? could you grade? could they grade?
V-ing form
could I be grading? could you be grading? could she be grading? could we be grading? could you be grading? could they be grading?
Perfect
could I have graded? could you have graded? could she have graded? could we have graded? could you have graded? could they have graded?
V-ing perfect
could I have been grading? could you have been grading? could she have been grading? could we have been grading? could you have been grading? could they have been grading?
Interro-negative form
Simple form
could I not grade? could you not grade? could she not grade? could we not grade? could you not grade? could they not grade?
V-ing form
could I not be grading? could you not be grading? could she not be grading? could we not be grading? could you not be grading? could they not be grading?
Perfect
could I not have graded? could you not have graded? could she not have graded? could we not have graded? could you not have graded? could they not have graded?
V-ing perfect
could I not have been grading? could you not have been grading? could she not have been grading? could we not have been grading? could you not have been grading? could they not have been grading?