I said that I was going to defend Joel Marks - at least on the essentials. Here goes. I'll deal separately (in a later post or posts) with the criticisms made by Jerry Coyne and Jean Kazez. For now, I just want to say why I think Marks has it basically right. (I see that he's writing a book on the subject - I'll be very interested to read it, especially as one of my own ambitions in the medium term is to write a book on the same issues.)
In sketching why I think that Marks is essentially right, I'm going to return to my favourite example, what it means to say, "This [pointing to my 2009 Honda Civic, perhaps] is a good car." The best idea I can come up with - assisted by philosophers before me - of what this means is, "This car possesses the set of properties that we want in a car." It's easy enough to see how the "goodness" of a car, if that is what car-goodness is about, can, in the right circumstances, motivate me to buy a certain car, to want to drive in or ride a certain car, and so on. The property of goodness already has my wants built into it.
But there are some important points to note about this. First, if my translation of "This is a good car" is correct, then I am not breaching Hume's law by going from "is" to "ought" without invoking a desire along the way. Hume didn't deny that you could do that. He thought that you can't go from "objective", desire-free is's to oughts. A property such as goodness, which has our wants or desires built into it, certainly can ground an "ought", and Hume knew this.
Second, if my translation is correct, car-goodness is not a property that is "out there", independent of our desires. Yes, the car may have the properties that we want in a car. But what those properties actually are will depend on us, and, more specifically, on what we do actually want in a car. If we change our minds about what we actually want in a car, then the car may cease to possess the summing-up property of car-goodness, even if there's a sense in which car itself hasn't changed (it is just as comfortable as it always was, has the same performance characteristics, the same fuel consumption, the same level of reliability, and the same underlying physical characteristics such as shape, mass, and so on). Whether or not the car possesses car-goodness - the property of having the properties that we want in a car - will depend on, among other things, our desires.
Third, strictly speaking there is probably no "we" here. There might be - it is possible that everyone involved in the conversation wants just the same thing in a car. In a very small group of like-minded car enthusiasts, that might be very close to being the case. But in practice, this "we" is likely to be a fiction. There may be a lot of agreement about what the people speaking and listening want, but it will not be total agreement, and the people who want some different combination of properties from the majority are not just wrong (in the way that someone can be just wrong about, say, the car's mass).
Despite these points, and doubtless other related ones, we find it very convenient to talk about whether or not a car is a "good" one. And yet, we all know, if we think about it, that this is pretty much a fiction, partly because "we" are a fiction - there just is no "we" who all have exactly the same wants in a car. Okay, in some social situations we might all want exactly the same thing in a car, but that is unlikely in practice even in a small group of people. On the internet, for example, it is vanishingly unlikely.
We all know these sorts of things, at least if we think about them, but it remains convenient to talk about a car being, or not being a "good" one. One reason for that is, despite everything I've said above, there is still a lot of agreement about what we want in a car (at least that is going to be so in many social contexts), so much so that is easiest to act on the basis that we really do agree on what is important and can sum it up reasonably unproblematically.
Of course, as is shown by real-world arguments between spouses or lovers about what car to purchase, there may be limits to the tacit consensus. But usually at least a rough consensus can be presumed. And there are reasons for this - given the kinds of organisms we are, given the way our societies are structured, and so on, it's not surprising that we want comfort and find similar things comfortable, that we want fuel economy, reliability and so on. It's more likely that we'll disagree about how to weight these various properties than that we'll disagree about them totally.
In the end, our judgments about the "goodness" of a car are not just arbitrary - not just anything is going to count as goodness in a car - but nor is car-goodness a property that is "out there" independent of our desires.
When I choose a car, do I really need to measure its car-goodness? Not really. All this talk about "goodness" is socially convenient, but in the end I can simply choose the car that has the properties that I want in a car (as well as being affordable and so on, if we don't count those as properties of the car). I can go through life not thinking in terms of car-goodness, as long as I am clear on what I want in a car (including how much weight I place on such things as reliability, comfort, fuel economy, various aspects of performance, and so on). I can weigh all this up without ever even needing to use the word "goodness", much as the word may provide a convenient way of speaking in social situations.
I don't see the need to abolish the word "good" when speaking of cars, but nor, strictly speaking, do I need to use it when considering what car to buy. It's all good (as it were!). But if I thought that my own judgments of goodness were rationally binding on everyone else - that "goodness" is like mass, a property that is independent of our desires, and about which someone can be just factually wrong - then I'd be making a mistake.
When it comes to moral language, such as the language of moral forbiddenness, moral permittedness, etc., this may likewise be socially convenient, but there seems to be a much greater tendency for people to think that these are properties which are "out there", independent of our desires, that people can be just wrong in a way that they can be about a car's mass, that judgments of these things are binding on others with different desires (values, hopes, fears, etc.), on pain of being just mistaken. All of this, I suggest, is an illusion.
Not only that, Joel Marks is quite correct that I can go through life without needing the language of moral forbiddenness, etc., when making judgments about how I will live my life, what laws I will support and so on. I can think more directly about what courses of action or laws, etc., have the properties that I want in such things (such as the property of being likely to achieve my own ambitions, the property of conducing to the happiness of my loved ones, the property of not adding to the world's suffering, and so on). I can weigh all this up quite directly without having to invoke further properties of moral forbiddenness, and so on, which sum over these other properties.
Marks is also correct that it may, in many cases, be more effective to get people to change their minds about some course of action if we discuss the objective properties of the course of action (such as its propensity to cause or ameliorate suffering) than if we use language such as "morally required" or "morally forbidden". Perhaps there are also cases where the latter language is just too convenient to forgo, or where it is just too complicated and inconvenient trying to speak in some other way. That might be so, for example, when we are speaking to young children. But if we are aware of the issue, we may be better placed to make rational decisions for ourselves and to persuade others to make what we regard as "good" decisions.
There's a lot more to say, of course. It's no wonder that Marks wants to write a whole book on the subject - and that I do, too. But I do think that Marks is essentially correct, and I agree with the point that Jean Kazez (I think it was) made on the earlier thread that it's no criticism of Marks that he goes on making much the same choices as he used to. Of course he does - just as I would go on choosing the same cars whether or not I naively believed that there was an objective property of car-goodness "out there", independent of my desires. When he does so, however, he may see more clearly what he is actually doing, and this may help him make better (!) decisions and be more persuasive when he tries to influence the decisions of others.
We'll doubtless get to some criticisms in the comments, and in later posts, but I think that Marks is basically on the mark.