Never before in the history of mankind has there been a period when hitherto accepted moral principles have been more severely tested. The agonized cry of a world smitten by two major wars in a handful of years leaves no doubt in the minds of many that natural law ethics, ifit is to have relevance and to survive, must provide at least the outline of an answer to the problems of every day living. To date, many hundreds of books and articles have been written setting forth with great eloquence the basic and immutable principles of natural law ethics. But too often these discussions fail to consider, in their agonizing detail, situations where there is a choice between conflicting values, conflicting loyalties, conflicting ideas and duties, each of which has a claim to recognition. It is only in the isolation of the particular case that the frightening dilemmas of natural law can be most clearly experienced. To give just two illustrations.I. The Nature of the Problems and Some Previously Suggested Solutions.- I. An outline of the problems to be considered.- II. An outline of some contemporary writers.- III. A statement of the problems to be solved, and the procedure to be followed.- II. An Examination of the Concept of Self Evidence in Thomistic Natural Law Teaching.- I. The nature of the problem, some preliminary considerations, and an outline of the procedure to be followed.- II. S. Thomass teaching concerning the concept of self evidence in natural law precepts.- III. The role of the Thomistic concept naturalis inclinatio in our knowledge of self-evident natural law precepts.- IV. A critical assessment of some of the precepts suggested by contemporary writers as being self-evident, together with a summary of the main findings of this chapter.- III. The Thomistic Distinction Between Primary and Secondary Natural Law Precepts, as Found in the Commentary on the Sentences, the Summa Contra Gentiles and the Commentary on the Nicomachean Ethics of Aristotle.- I. RecalÉ