In most fields of philosophy, a set of propositions that entails a contradiction is held inconsistent, following the law of non-contradiction.1 Where one can rank the support for the various propositions, this allows the figure of indirect proof: if adding a proposition to a set of beliefs singly better supported than it produces a contradiction, the proposition added must be considered false.2
In one field of philosophy, however, most people seem to hold this method of reasoning invalid: ethics. Many proposed ethical systems place upon people burdens to two or more incompatible actions. Elsewhere, such a system would be held inconsistent, and in need of alteration. In ethics, however, the law of non-contradiction does not seem to apply: an actor faced with contradictory obligations should follow one, considering his violation of the other a necessary evil, regrettable but not fatal to the system.3
This strikes me as exceedingly sloppy reasoning. We do not hold that although Newtonian physics and relativity are contradictory, they are both true and we should follow one, considering our denial of the other necessary to avoid indeterminacy; we hold that the contradiction renders any belief in both necessarily false. So it should be in ethics. There are no necessary evils; only false ethical systems that produce them. The true ethical system will at no time obligate an actor to two incompatible actions. This does not mean, of course, that I believe that, a priori, if an ethical system is to prohibit, for example, lying, it must do so in all circumstances; that prohibition may have exceptions (“One may not lie except to criminals”, or even “One may not lie except when doing so is commanded by a higher principle”, with the precedence established).4 However, these exceptions must be inherent to the original ordinance, and not produced from the conflict of absolute ordinances.
Law being a subset of ethics governing enforceable interpersonal interactions, rights are also subject to this prohibition of contradiction. No right may be justly violated at the instigation of any other ethical principle. Thus, long lists of “human rights” such as those of the UN are necessarily false, for they place agents under competing ethical claims. Even the rights to free speech and freedom of property are inconsistent, as in the stock case of crying “fire”. Traditionally, it has been held that in this case the latter right overrides the former. I say, on the other hand, that this instead means that one of these rights is not a true right, but rather a manifestation of something else. Legal questions must be solved by argument from sound principles, not by weighing of incompatible principles in incommensurate units.
1: A strong contradiction is, however, necessary. A set of propositions that produces a paradox is not inconsistent unless the addition of other certain premises produces a strong contradiction.
2: Note, however, that this also applies to the better-supported premises; their contradiction of a supported premise lowers their support correspondingly, even though from the assumption that they are better supported than the new proposition their support remains positive. Thus, one cannot use a set of propositions to disprove a large number of propositions only slightly less-well supported; even though it is more plausible that any one of the introduced propositions be false, it is more plausible that some proposition in the original set be false than that all of the introduced propositions be false. Thus, the set of propositions believed true should be the set that minimizes the combined evidence in favor of propositions believed false.
3: And it is not clear to me why he should do one instead of the other. If government is a necessary evil, unjust but necessary to prevent other injustices, why should we not hold that the injustices consequent on the absence of government are a necessary evil, unjust but irremediable without other injustice?
4: This is ultimately the problem with Kantian ethics and rule utilitarianism. Kant’s categorical imperative may be valid in principle (and is a necessary consequence of moral absolutism), but his use of it to obtain, for example, an absolute prohibition on lying ignores that the true rule of behaviour is not necessarily “lying is acceptable”, but rather “lying is acceptable in this situation”, which one could wish to be a universal principle of action without the consequences attending permission of lying in general. Similarly, for any proposed rule under rule utilitarianism one could propose the modified rule that the previous rule is to be followed except when violations of it would improve utility. The rule utilitarian would then have to say that there is no such instance, which requires much stronger support (and, arguably, moves rule utilitarianism indistinguishably close to deontology, merely approaching from the opposite side (assuming the consistency principle)).