{ 1 } - They say that virtue is more basic, since how one OUGHT to act can be defined as how a virtuous person would act, when correctly understanding the situation and acting in character.
{ 2 } - They say that duty is more basic, since a VIRTUOUS person can be defined as one who has internalized the correct principles about how one ought to live; so to have the VIRTUE of gratitude is just to have internalized the norm that we ought to return good to those who have done good to us.
{ 3 } - They say that virtue and duty are interdefinable -- and so neither is more basic than the other; instead, both are different sides of the same moral coin.
{ 4 } - Philosophers disagree about this.

It's significant that almost all moral philosophers, regardless of their perspective (from cultural relativists to utilitarians or whetever) have brought both virtue and duty into their discussions.