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