The concept of duty is composed of three elements: a moral authority, a norm enacted by the former, telling others what should be done or omitted and a belief in the necessity of strict obedience by the members of community. The Greek had no concept of duty, as they favoured independence of mind and moral autonomy as main features of the good citizen. Nowadays a great number of terms with Greek origin are used in order to deduce a theory of duty. However, it must not be forgotten that terms do not have fixed meanings but practical use. The mentality of the past should not be inferred from our modern thoughts.