This area specifically is very confusing to me.
5.1. THE VALUE OF LIFE
I said earlier that what is wrong with Rand's attempted derivation of ethics is that it requires the evaluative presupposition that life is good, which has not been and cannot be inferred purely from observations. Some Objectivists say that life actually isn't good, but everything which promotes life is good. I think this (i.e. the first part of that claim) is obviously false, besides being a distortion of Rand's views, but not to press that - this view has the same problem as all attempts to bridge the is/ought gap, i.e., it just raises the question, how do we know that what promotes life is good?
One way to answer this might be to say that this is just the meaning of "good", i.e. "good" just means "promotes (my) life."
If you take the Objectivist theory of meaning, however, which rejects the analytic/synthetic distinction and identifies meaning with reference, then this sort of answer cannot be legitimate. It cannot ever be legitimate to answer "How do you know that A is B?" by saying that this is implicit in the meaning of "A". For on the Objectivist theory of meaning, everything that is true of A is implied in the meaning of "A", and everything that is not true of A contradicts the meaning of "A". Therefore, if something's being implied in the meaning of our words was a sufficient explanation for how we knew it, we would be omniscient. That is, if we know every fact that is implied in the meanings of our words (every fact the denial of which is contradictory), then, if the Objectivist theory of meaning is also correct, we know every fact. Since this is not the case, the Objectivist has to say that even the things that are implied in the meanings of our words need to be proven - specifically, they require observational evidence. For example, when asked how we know that gravitational attraction is inversely proportional to the square of the distance between the bodies, it is not correct to say we know this because the denial of it is contradictory. The denial of it is contradictory, on the Objectivist theory, but that does not explain how we know it. To explain how we know it, one would have to detail certain scientific experiments and observations of the solar system. For the Objectivist scientist, to defend a theory by saying the denial of it is contradictory, is just begging the question. We don't know whether it is contradictory until we first find out whether it is true.
Thus, it can not be an adequate answer to my question, "How do you know that what promotes life is good?" to say that the denial of this proposition is contradictory or that it is implied in the meaning of "good", if the Objectivist theory of meaning is correct. For such a reply would simply beg the question - the denial of the proposition in question is a contradiction, on the Objectivist view, if and only if it is true that what promotes life is good. We still need an explanation of how we know it is true - i.e., what observations lead to this conclusion, and exactly what is the form of the inference by which they lead there. In other words, even if "good" means "promotes life", on the Objectivist epistemology and philosophy of language, you still have to prove that this is what "good" means, by empirical (sensory) evidence. I have never seen such a proof.
On the other hand, suppose we take up my theory of meaning, in which there is an analytic/synthetic distinction, and only a small subset of all true propositions are analytic (i.e., such that their truth is implied in the meanings of the words involved and such that their denial is contradictory). In that case, it does not beg the question to say that we know what serves life is good because this is the meaning of good, because what the word means can be known immediately, by reflection (without this leading to omniscience) - at least, you can know what you mean by a word by reflection, although you need empirical evidence to determine whether others mean the same thing. However, the reply now faces a different problem: The claim that "good" means "promotes life" is now simply false, and it is refuted by Moore's 'Open Question Argument'. That is, given that we make a distinction between the analytic and the synthetic, we can repeat the "Jocasta/Oedipus" argument to show that "promotes life" does not mean the same as "good". Consider a person who decides to commit suicide. This person believes (let us suppose) that
(G) Ending his life is good.
But he does not believe that
(P) Ending his life promotes his life.
since he knows that ending his life will destroy his life. It is evident, then, that "good" can not mean the same as "promotes life," for the same reason that "Jocasta" can not mean the same as "Oedipus' mother." (It means something more like "worthy of being chosen" - though I would not claim this is a completely accurate definition either.) It is possible for a person to not know that what promotes life is good, just as Oedipus did not know that Jocasta was his mother. Therefore, some explanation is required of how we find out that what promotes our life is good.
Note that when I say "an explanation of how we know this" is required, I am not expressing doubt about it. I mean simply what I say: given that we know it, how do we know it? Do we know it based on observation, or do we know it a priori? If we do know it, but no observations can be found sufficient to justify it, then we must conclude it is a priori. That is the point of the present discussion.
In more general terms, you can see that this sort of appeal to the meaning of "good" can not be valid, since if it were, it would be a way of 'validating' any claim whatsoever. Any person could take whatever ethical views he has, and claim that they are true in virtue of the meaning of good. I might propose to define "good" to mean "promotes the production of chocolate ice cream," and thence deduce that every person ought to produce as much chocolate ice cream as he can. This is silly, of course. I can't simply claim that this is what "good" means. It is not what "good" means, and if I want to claim that producing chocolate ice cream is good, I need to give a substantive reason for thinking so. And the same holds no matter what is substituted for "chocolate ice cream." Claiming that "good" means "promotes x" is not a way of showing that it is good to promote x.
Similarly, one could use the strategy to validate any descriptive claim. Suppose I want to show that the sky is red. I say, "Well, 'red' means the color of the sky during the daytime." That is not what "red" means, and that does not give a reason for thinking the sky is red. Nor does the parallel validation work if you substitute "blue" for "red". If asked how I know the sky is blue, I also can not merely say, "'Blue' means the color of the sky during the daytime." That isn't the meaning of "blue" either, and it is not a reason for thinking the sky is blue. The only reason for thinking the sky is blue consists in going outside and looking up. You don't define the sky to be blue. You observe its color.
About my proof that everyone should produce chocolate ice cream: an Objectivist might say that the difference there is that he (the Objectivist) has given a correct definition, because it really is good to promote life, whereas the proposed ice-cream definition is not correct. But this just begs the question - how do you know that your definition is correct, and not the chocolate-ice-cream definition? Of course, anyone with any ethical views whatever is going to claim that his views are correct, and therefore, if the Objectivist strategy is permissible, may propose a 'definition' of good that makes his theory of ethics necessarily true, and may respond to all objections in exactly the same manner the Objectivist can.