1. Why should the fact that physics fixes all the facts make it hard to find room for moral facts? If physics fixes all the facts, then if world B is a microphysical duplicate of world A, then A and B are duplicates with respect to all the facts, including the moral ones, if there are any. Physics fixing all the facts implies that any non-physics facts must at least supervene on the physical facts, which is to say that things cannot differ in any way without differing physically. So situation x cannot differ morally from situation y unless there are physical differences between x and y. This is innocuous and tells us nothing about what kinds of facts there are. Rosenberg here seems to treat the claim that physics fixes all the facts as though it were the much stronger claim that all the facts are facts of physics. If all the facts are physical facts then it’s hard, in fact impossible, to find room for moral facts, since no moral facts are physical facts.
2. Nihilism, I take it, is the view that there are no moral facts: no moral statement is true, e.g., it is not true that one ought not to eat babies. This is no more true than the claim that one ought to eat babies. (I’m assuming that there being a fact that P is the same as it being true that P.) There just isn’t anything that morally one ought, or ought not, to do. If nihilism is true, it’s not because physics fixes all the facts.
3. The no coincidence argument:
As a result of natural selection humans are innately disposed to believe certain things. It would be wildly coincidental if these beliefs were true independent of this evolutionary history. If moral beliefs are true, then they are true of reality, independent of our evolutionary history. Our moral beliefs are products of our evolutionary history. Therefore, nihilism is true: there are no true moral beliefs.
If this reasoning were sound, it would justify many kinds of nihilism, e.g., humans are innately disposed to believe that dogs give birth to dogs and cats give birth to cats, and not the other way round. Yet it is true that dogs give birth to dogs and false that cats give birth to dogs. This is true independent of our evolutionary history. Sometimes the best explanation of why we have been selected to believe certain things is because they are true, and true beliefs about some matters enhance fitness. The fact that we were naturally selected to believe that there are things we ought to do, or not do, irrespective of our desires, supports nihilism only if there can be no such facts in a world where all facts are fixed by physics. If we can’t reasonably believe that natural selection has endowed us with some capacity to know the world then total skepticism is inescapable and we are no more justified in believing the well-confirmed theories of science than anything else. The Neurathian boat in which natural selection has launched us might be pretty leaky, but we have to think it keeps us afloat! (“We are like sailors who on the open sea must reconstruct their ship but are never able to start afresh from the bottom. Where a beam is taken away a new one must at once be put there, and for this the rest of the ship is used as support. In this way, by using the old beams and driftwood the ship can be shaped entirely anew, but only by gradual reconstruction.” Otto Neurath, 1882-1945)
4. However, there is a good reason to doubt that there are such facts because, as Rosenberg says, that they all rely on false presuppositions. If it is true that someone ought to do x, then he has good reasons to do x. (On one account, this is what is means to say that he ought to do it.) However, any reason he has to do something is rooted in his desires. No practical reasons are grounded in objective reality; the fact that such and such is true of the world in itself creates no reason to do one thing or another. That fact must connect to what one wants. Natural selection has installed in us the illusion that certain objective facts constitute reasons to behave in certain ways, particularly when we have competing reasons not to do so. This internalized constraint on self-interest is the “aim” of human moral psychology. Objective reality has nothing to say about what one ought to do, but human minds, adapted to social life where constraints on self-interest promotes inclusive−but not necessarily individual−fitness, project the moral ought onto the world. Evolution has equipped us with the disposition to categorize social reality in moral ways, e.g., to identify some acts as unjust. And that judgment generates the conviction that we ought to do something about it, the feeling that one has a reason to do something about the act just because it is unjust. The presupposition of all moral claims, that there are reasons to act “out there” in reality, is false. For some, this suffices for the conclusion that all moral claims are false, i.e., nihilism. This conclusion is sometimes called fictionalism, and its adherents often contend that while morality is a fiction, a kind of illusion, it is a useful one. If so, then what we want gives us good reasons to act as though we believe that there are reasons to act independent of anything we want.
5. However, we must accept fictionalism only if belief in moral facts cannot survive the realization that there are no practical reasons built into the fabric of reality. Our longstanding concept of moral fact includes the idea of an objective state of affairs that presents us with reasons to act. Nothing actually falls under this concept so either there are no moral facts, and the concept should be abandoned, or our concept of moral facts must be revised. This is an instance of an important question that arises often in the attempt to find a place for what’s important to humans in the world science portrays: when have we discovered that things of a kind do not exist, since nothing has property F, which we have always regarded as essential to being a thing of this kind, and when have we discovered that we were wrong to believe that things of this kind must have property F? The answer is not always obvious. Perhaps we can reasonably continue to believe that there are moral facts even as we abandon the illusion that they impose upon us reasons for action that are ultimately independent of our desires. (Across the board, Rosenberg seems strongly drawn toward abandoning, rather than revising, our concepts. Thus, e.g., not, “We’ve found out that our behavior is causally determined, so we were wrong to assume that no determined behavior is free,” but, “We’ve found out that our behavior is causally determined, so we are not free.”)
My inclination is to reject moral nihilism, and to assert that there are moral facts but that they provide us with reasons to act independent of our desires is an illusion courtesy of natural selection. I’d say that what all this amounts to is the discovery that the moral truth is relative to the human species, not to there being no moral truth. It puts morality in its natural, human place, deflating its pretensions to transcendence. But whether the Christian can reasonably welcome this kind of relativism (or Rosenberg’s nihilism), or reasonably hope to avoid it, is a question that deserves a fuller answer.
Rosenberg’s approach is to accept moral nihilism, because there are no moral facts that provide us with reasons to act independent of our desires; that’s an illusion courtesy of natural selection.
Either way, I think Rosenberg is right to say that all this has no serious deleterious effect on moral motivation; that “nice nihilism” is the likely and reasonable response. We may note that the analogous realization that disgustingness is not a feature of objective reality, but the projection of a response natural selection has programmed us to have back onto the world, is not likely to move us to eat things that disgust us.