It is commonly believed that moral rules, principles and standards play an important role in the process of law application. Two obvious examples can be pointed out here (Gizbert-Studnicki and Pietrzykowski 2004, pp. 64–70). The first is related to the judicial decision-making process in particular cases in which a judge has to apply legal norms that include moral concepts such as “good faith”, “reasonable care”, “social justice”, “human dignity” etc. The second example refers to the constitutional courts’ decisions on the constitutionality of legislative acts (statutes). In such a case, the moral rules, principles or standards can constitute the criteria of legal validity. Generally speaking, the influence of morality in the legal domain is a phenomenon that is under constant investigation by the legal sciences. As Moore convincingly argues, we can distinguish at least seven relations between law and morality that contemporary legal philosophy deals with (Moore 2012, pp. 436–443). What is more, many influential legal philosophers claim that morality—moral principles, rules or standards—can (the inclusive legal positivists, e.g., Coleman, Waluchow, Kramer and Moreso) or have to (the non-positivists, e.g., Dworkin, Dreier and Alexy) be incorporated into the law. The so-called Incorporation Thesis is often questioned by the supporters of exclusive legal positivism—for instance, by Raz (1994, 2004, pp. 1, 7–17)—however, it is worth noting that even the representatives of such a hard version of legal positivism provide the reasons against the classic positivistic Separation Thesis (Green 2008) or argue for certain interpretations of the Necessary Connection Thesis (Raz 2009, pp. 167–169, 179–181).

I do not want to enter into a probably pointless discussion here that leads nowhere on whether the positivistic Separation Thesis is true or the non-positivistic Necessary Connection Thesis is more plausible. In my opinion, despite disregarding this fundamental jurisprudential controversy concerning the nature of the relations between law and morality, it is methodologically acceptable that we directly focus on a very important, specific practical problem: the validity of moral rules and principles. This problem is usually treated as a philosophical, psychological or sociological one (Maluschke 2007). In what follows, I will propose a somewhat unorthodox approach by analysing this problem from the legal point of view—more precisely, from the point of view of a law-applying agent, especially a judge.

Naturally, it can be questioned that the approach adopted herein is “unorthodox” in effect. If we consider the well-known test of institutional support and the co-related concept of the sense of appropriateness (Dworkin 1977, pp. 40–41, 64–68), it can be argued that the legal (or jurisprudential) approach to the problem of the validity of moral rules and principles is not innovative at all. Yet this statement seems to be incorrect. As Putnam (1995, p. 5) rightly reconstructs Dworkin’s view on the relation between legal validity and moral validity:

[W]hile legal validity and moral validity unquestionably differ […], still, in what Dworkin calls “hard cases” […] the judge is obligated to decide in such a way that the outcome is the morally best possible, given the constraints imposed by the system. In effect, moral thinking replaces legal thinking, at least in arriving at the decision (and perhaps even in justifying it) in “hard cases”.

Thus, the “unorthodoxy” of our analysis consists, in fact, that in what follows, juristic thinking replaces moral thinking: some jurisprudential ideas will be used to explicate the problem of the validity of moral rules and principles.

Before going into detail, a brief description of the normative situation of a law-applying agent is necessary. The problem of the validity of moral rules and principles becomes legally important in any case involving the application of law in which a judge (or any law-applying authority) is obligated to take into account moral rules, principles or standards. At this point, two normative situations have to be contrasted. The first is when a given moral rule, principle or standard has already been incorporated into the law—for instance, when it is frequently used by the judiciary. And the second concerns when such incorporation has not yet taken place. In this context, it has to be stressed that our analysis refers exclusively to the second case, because in the first situation, we should rather speak about the “legal validity” of the moral rules and principles that have already been incorporated into the legal system. In other words, we are only interested in such an “original normative situation” in which a law-applying agent has to take into consideration a certain moral rule or principle for the first time; a rule or principle that cannot be simultaneously classified as a legal one (or as legally valid).

It can be assumed that a law-applying authority that is obligated—during the process of legal decision-making—to take into account morality, will direct her/his attention to the set of valid moral rules and principles. Hence, the issue of the validity of moral norms arises as a legally relevant problem. However, it is obvious that the validity of moral rules and norms has to be analysed in a different way than in the case of the validity of legal norms. For instance, the juristic conception of the systemic validity of law, commonly used in legal practice, and based on the concept of a due enactment and some formal criteria of legal validity (Wróblewski 1988, pp. 96–98), is probably completely useless in reference to the extra-legal moral rules and principles. Therefore, the starting point of the analysis has to consist in the careful identification of the most fundamental questions that have to be answered by the law-applying agent who is obligated to take into consideration valid moral rules and principles. However, it should be noted that we will identify these questions per analogiam to the questions that are typically articulated concerning the problem of legal validity, thus replacing moral (ethical, philosophical) thinking with juristic (legal) thinking.