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CHRISTIAN MORAL PRINCIPLES

Chapter 7: Natural Law and the Fundamental Principles of Morality

Summary

Much Catholic teaching on natural law refers to the work of St. Thomas Aquinas, and Vatican II commends him as a guide. We can therefore examine his treatment of natural law to see how the Church views the subject.

“Law” for St. Thomas primarily means a reasonable plan of action. He begins from what he calls the “eternal law”—God’s plan in creating and redeeming. Any other reasonable plan of action must somehow derive from it. People can plan their lives reasonably only because, in one way or another, they share in the universal plan present in God’s law; to the extent they try to follow some other plan, their lives are unrealistic.

Human beings, according to St. Thomas, are naturally disposed to understand some basic practical principles. These are the primary principles of natural law—what St. Paul calls the law written in one’s heart (see Rom 3.14–16). However, truths of natural law, including specific norms, are also part of revelation. As Vatican I says, this is in part so that “even in the present condition of the human race, those religious truths which are by their nature accessible to human reason can readily be known by all men with solid certitude and with no trace of error” (DS 3005/1786; translation supplied). Thus natural law and divine law can be distinguished, but not separated and opposed.

Practical thinking is reasoning and judging about what might and ought to be. According to St. Thomas, its first principle is: The good is to be done and pursued; the bad is to be avoided. Scholastic natural-law theory formulated this as a moral imperative: Do good and avoid evil. But, as Thomas’ formulation shows, the first principle is not a moral norm. It expresses the intrinsic, necessary connection between human goods and actions which bear upon them; in thinking about what one might do, it is impossible to disregard entirely the goods and bads...