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