In Aristotle’s thought, economic activity refers to a kind of praxis consisting in allocating the human and material means that constitute the oikos –the domestic community- to fulfil its natural ends: ensure both life and the means of life. By means of natural chrematistics -acquisitive art- families acquire the necessary means for this, which come from production and exchange. Families group together in the political community (polis) whose end is living well, according to virtues, among which justice is highlighted as the ‘complete virtue’. For its part, the Christian êthos regards every human act, internal and external, of this complete system (polis, oikos and chrematistics) as tending towards its ultimate purpose (beatitudo). In St. Thomas’s view, eternal law harmonizes necessity of irrational beings, loving God’s action (divine law), natural law, and the contingency of ‘human things’ where the economy is included. Trading activity is lawful if it is at the service of the oikos or polis and according to how is exercised, by following commutative justice. The family, political and religious character of human nature establishes what the natural-necessary consists of, embracing, apart from bodily goods, others derived from considering social status and the life chosen (civil, religious, active or contemplative). Economic activity based on this anthropological root has a specific place as a part of an ordered natural-legal totality that provides the economy with meaning and sufficient moral guidance.