To call something valuable is to say that it has other properties that provide reasons for behaving in certain ways with respect to it. (Scanlon, T.M., 1998. What We Owe to Each Other. Cambridge, Mass: Harvard University Press.)We'll get this out of the way immediately - there are no such properties that provide reasons for behaving in certain ways.
Still, this is supposed to provide a way of answering Mackie's claims that there are no objective values. It does so by asserting that certain objects of evaluation have properties that give people reason to respond in a certain way to them; and that objects of evaluation are "good" or "bad" according to the type of attitude or behavior that its properties give rise to.
Michel Smith calls this "The Reasons Approach" (Smith, Michael, "Beyond the Error Theory," in A World Without Values: Essays on John Mackie's Moral Error Theory, (Richard Joyce and Simon Kirchin, eds.), 2010.)
Because these properties are in the object, and because they rationally demand a particular attitude or behavior, all people should have (are rationally required to) have the same response.
Technically, the properties in the object of evaluation do not directly cause a particular response. Instead, they rationally require a particular response. It is still possible for an individual to become aware of the properties that demand a particular response and not respond appropriately. However, those people are irrational in some way.
Michael Smith attempts to explain this by showing how the process works for belief. If an agent has a belief that P, and a belief that P implies Q, then there exists a requirement of reason that the agent believe that Q. This is because beliefs aim at truth, and the two premises provide reason to believe that Q is true. Consequently, these two beliefs create a rational requirement to believe that Q is also true.
The problem with this Reasons Approach to answering Mackie is that we cannot come up with a similar type of relationship between beliefs about the properties of things and having a particular desire. The rational requirement to believe that Q comes from the fact that the aim of beliefs is truth. What is the aim of desire such that there can be a rational requirement to adopt a particular motivation towards a state of affairs based on beliefs regarding its properties?
If we say that desires aim at satisfaction, then this does not yield the conclusion that there are properties in the object of evaluation that warrant a particular motivation. The desires have to aim at something in the object of evaluation itself.
Smith examines the possibility that desires aim at "the good". However, this would result in a viciously circular set of claims.
It would be viciously circular to explain why a consideration is a reason for desiring in terms of the fact that the good is the aim of desire and then to immediately go on and explain the good in terms of what there is reason to desire.An object of evaluation has properties that generate rational requirements to have particular desires, because those desires aim at objects of evaluation that have properties that generate those rational requirements.
Coming up with a property that generates reasons to be motivated in a particular way ultimately seems to require some sort of non-natural prescriptive property in the object of evaluation - the type of entity that Mackie says does not exist. The task of explaining how a natural property can generate reasons to be motivated in a particular way seems unlikely to succeed.
I hold the position that properties that generate reasons to be motivated in a particular way towards them do not exist. Evolution has molded our desires in such a way that they generally bring about behaviors that result in genetic replication. This does not mean that genetic replication is the aim of desires (the way that truth is the aim of belief). Genetic replication is an unintended side effect. However, it is a type of side effect that nature uses to select for tendencies to form certain desires and aversions.
In the case of humans, evolution has given us malleable desires - desires that are changed through our interaction with the environment. This allows us to adapt to a number of different environments, rather than having us hardwired to fit into a specific environment. These "interactions with the environment" include interactions with other people. Those people have reasons to promote certain desires in us, just as we have reasons to promote certain desires in them. It is from here that we get morality - not from "properties that provide reasons for behaving in certain ways with respect to it."