English verb conjugation
CAN REFER

Regular verb: refer - referred - referred

Affirmation

Simple form	V-ing form
I can refer you can refer he can refer we can refer you can refer they can refer	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	V-ing 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	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	V-ing form
I cannot refer you cannot refer he cannot refer we cannot refer you cannot refer they cannot refer	I cannot be referring you cannot be referring he cannot be referring we cannot be referring you cannot be referring they cannot be referring
Perfect	V-ing perfect
I cannot have referred you cannot have referred he cannot have referred we cannot have referred you cannot have referred they cannot have referred	I cannot have been referring you cannot have been referring he cannot have been referring we cannot have been referring you cannot have been referring they cannot have been referring

Interrogative form

Simple form	V-ing form
can I refer? can you refer? can he refer? can we refer? can you refer? can they refer?	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	V-ing 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?	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	V-ing form
can I not refer? can you not refer? can he not refer? can we not refer? can you not refer? can they not refer?	can I not be referring? can you not be referring? can he not be referring? can we not be referring? can you not be referring? can they not be referring?
Perfect	V-ing perfect
can I not have referred? can you not have referred? can he not have referred? can we not have referred? can you not have referred? can they not have referred?	can I not have been referring? can you not have been referring? can he not have been referring? can we not have been referring? can you not have been referring? can they not have been referring?