The Normative Contingency Thesis (NCT) is a compelling objection to Moral Realism.

Okie dokie. http://www.youtube.com...Based on R1, most of the groundwork for my case has already been laid. First, recall the definition of realism:1. Ethical sentences express propositions. 2. Some such propositions are true. 3. Those propositions are made true by objective features of the world, independent of subjective opinion.In particular, the realist's commitment to the third proposition is what's damning, because therein lies the origin of the justificationalist structure that makes the position untenable. This is due to...Normative ContingencyNobody will contest that moral propositions require justification--like epistemological questions, moral propositions require an underlying substance for validation. If one claims, for instance, that one ought not murder others, the curious individual might be inclined to ask, "Why?" The answer might be something like "Because murder is wrong", or "Because human life is valuable". Bridging the is-ought gap requires making explicit the hidden value judgment that unites some factical condition about the world with a normative claim about how that that world ought to be adjusted, and how its inhabitants ought to behave. This, I think, is uncontroversial. Just as nearly any epistemologist considers "justified true belief" to be at least necessary conditions for claiming knowledge, nearly any ethicist--in which group I'm sure my opponent, either by choice or by the circumstances of having to defend realism--will acknowledge the parallel burden of justification which rests on parties to an ethical discourse.Where other ethicists stop--and where I forge on--is the spot at which contingency seems to end. In epistemology, there is always some concern about infinite regress--asking "Why?" an infinite number of times when presented with any justification. Naturally, this leads to a problem--if all propositions require justification, but all justifications are swallowed in an infinite regression, what is left? As all roads are said to lead to Rome, so too do all propositions eventually reach a space where justification is no longer possible--you reach assertions, circularities, but never bona fide certainty. This, I contend, is an inherent flaw in justificationalist attempts to advance propositions, and it inheres just as surely in epistemic justificationalism as in moral realism. When you sufficiently scale back any derivational system of ethics, you reach some kind of "first principle" which gives rise to the network of deductions beneath itself. This, for most ethicists, is the spot where contingency seems to end.What happens, however, if you put that last meta-ethical proposition on trial? What is discovered about it? Well, you discover that it is also contingent; however, it is a different sort of contingency than that which characterizes the deductions contained in the system. Rather than being contingent upon some prior proposition or meta-ethical statement, it seems to be the last statement in the chain. So, upon what could it be contingent? The conditions of regress in epistemology may be helpful here: Infinite regress: given proposition P1, justify with P2. Justify P2 with P3, P3 with P4, ad infinitum. In other words, if all propositions require justification, the chain of exteriorities required to continue justification will stretch out infinitely. Vicious circularity: two propositions, A and B, rely upon each other for justification, establishing an endless loop of other-justification. That is, “A can be justified by reference to B; B can be justified by reference to A.” Axiomism: some particular proposition—P—at the "end" of a justificatory chain is asserted as self-evidently true, or is taken as given/assumed. “Given X, Y.” Alternatively, “X is useful/non-X is inconceivable; therefore, act/reason as if X.” The third condition, axiomism, seems to be the name of the game. Certain moral propositions are taken to be irreducible or axiomatic. Yet, this approach seems problematic. Drawing on the work of Kurt Gödel, all non-trivial axiomatic systems always have to refer to something exterior to themselves for validation--they cannot, colloquially speaking, "prove themselves". This, on my view, produces an interesting answer to moral irreducibility by extending the justificationalist quest beyond the limits of whatever is taken to be ethically axiomatic. One immediate problem with taking the axiomist route in ethics is the inability to distinguish reducible moral propositions from irreducible ones--if you have an ethical structure which is generically normative but absent of content, the axiomist approach conceivably allows one to supplement the "normative skeleton"--the generic normativity which has no content to transmit, and which is what realism seeks to defend in principle--with any meta-ethical content. If one is committed to the notion that ethical axioms have no justification but their own self-evidence, it seems essentially to be "deuces wild" on what kinds of meta-ethical assumptions we accept as long as we regard them as "self-evident". Hence, one could say something like "Well, if we just define morality as human flourishing, then we obviously have some clear answers", but that's precisely the problem--you could hypothetically define morality as more or less anything, or just collectively assume that a certain set of moral propositions is true, but this misses the point. Recall the third criterion of realism: 3. Those propositions are made true by objective features of the world, independent of subjective opinion. This, I think, is where the axiomist approach fails. Sticking to the Godelian formula, I think that, while first principles are asserted as axioms, they are actually contingent on the discursive fiat of the speaker(s). If a party to a moral discourse makes a meta-ethical assumption, and the rest of the group agrees with it, then it remains unquestioned and de facto axiomatic. But, especially given the interchangeability of meta-ethical "axioms", fiat and collective subjectivity don't pass the "objective features of the world, independent of subjective opinion" test. So, if at any point Con tries to define morality phenomenally--"If we just understand morality as..."; "This is how most ethicists reason anyway..."--then he can't win the debate because he's advocating constructivism, the view that normative constructs can be useful/preferable (although untrue), not realism. So, to sum up the case: 1. As with epistemology, ethical propositions require justification. 2. So, systems of ethical derivation are contingent on logically prior normative and meta-ethical propositions. 3. As with epistemology, justificationalism is structurally vulnerable to infinite regression, leading to circles, unjustifiable propositions, or claims to self-evidence/irreducibility. 4. First principles, which spawn systems of moral derivations, function as axioms in those systems; however, these propositions are easily interchanged, making it difficult or impossible to distinguish the reducible and the irreducible. These meta-ethical assumptions, rather than being objective/mind-independent, are actually contingent on subjective agreement; but, since realism requires objectivity/mind-independence, the normative contingency thesis seems to be a compelling argument for rejecting moral realism/justificationalist ethics. tl;dr You can keep asking people to warrant their ethical beliefs, and they'll eventually come down to some meta-ethical linchpin, e.g., "human life has value", which we have no reason to accept as true. They'll say it's useful, or that it "just is" true, or that it's true if you just define morality in a way that makes it so, but regression/contingency shows that even first principles are quick hide behind their natural subjectivity when put to the test.