Because moral truths must be truths about reality (as I have argued in my previous post) if we are to reject the subjectivist moral position, we have to define very carefully what we mean by saying that moral truths are objective.
We could mean that the moral truths are universal statements of goals. Subjective evaluative statements are statements of compatibility with subjective goals. To say "it's too cold in this room" is to mean "I want to feel comfortable, and in order for that to happen, the temperature in the room must be higher". Obviously, this is a subjective evaluative statement, since what's cold for you might be too warm for me because of our unique biology or mental reactions.
Saying "taking I-95 N from Boston is wrong" implies that you want to go south (e.g., to New York).
So, maybe all people have a certain set of goals, and to achieve these goals, they must do certain things having property of "good" and cannot do certain things thus having property of "bad". That would be interesting, but I don't think we would find such a universal set of goals for all humankind. In fact, quite the opposite: most people want to continue surviving and incur pleasure while staying away from pain. But what are we to do if people's goals intersect: i.e., if causing pleasure to myself will cause pain to you?
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What else we got? Well, we could define good as "beneficial". For instance, something good for a bacterium is to avoid destruction. For every living being there seems to be a set of goods and bads. So, just like we can recognize that certain things are good for us in the sense that they allow us to survive and enjoy ourselves, there are things that are good for others, both humans and other living beings.
One problem is with defining what exactly good is. Ayn Rand famously said that only living forms have a choice between staying living and being dead. Dead matter is already dead: it has no choice about it.
But surely one could argue that there is a difference between being a magnificent stalagmite and a bunch of crushed rock. So, we can define "good" and "bad" in terms of order vs. entropy. Order means good. Destruction of something means increasing its entropy. (Another objection to Rand is that humans can have other choices besides being alive or dead, such as leading more or less creative or rational lives, enjoying oneself more or less, etc. Those are real choices, and it's not clear one set of choices — e.g., how much fun to have in one's life — must be more important than another — how long to live.)
The problem is that the obvious fact of life is that in order for anything to survive it needs to feed on something else. We have to destroy plants and sometimes animals to survive; the animals do the same. Even the plants feed on the products of our sun's continued destruction.
So, is it good for a bear to eat me? It is good for the bear; it is bad for me. The same is true in reverse. So, again, how are we to decide between choices of good and bad? Should I steal someone's umbrella? It's bad to do that to someone else; but it's equally bad to let me walk under rain without an umbrella. Which bad should I avoid? Which good should I choose?
I do not claim that there are no answers to these question. I am trying to show that simply defining good and bad as harm and benefit does not suffice.
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One can go the route of moral intuitionists and say that "good" and "bad" are simple properties of nature as "red", "green", "hot", "cold" or having a certain electrical charge or mass or occupying certain amount of space. And we know these things simply from perception and do not have to define them in terms of anything else.
Here is my problem with this view of moral truths: it seems an intellectually arbitrary dead-end. All the physical qualities I listed above have relation to other events in the universe, can be investigated further, can be detected and verified independently. The same goes for mathematical truths, whatever one makes of them.
But if I am saying that "harming children for the fun of is bad; end of story", it doesn't seem like I can investigate the nature of this quality any further or connect it to other phenomena. I either believe it to be true or not. Maybe I can compare it with other similar truths ("Is it acceptable to allow three children of someone else to die at the cost of saving one's own single child?"), but it seems that the results of the comparison are themselves singular intuitive truths which one cannot investigate much further.
Also, this approach smacks of arbitrary ascribing of one's internal states to the nature without any way to verify the truth and validity of it. Imagine that I said that on a rainy day, the nature is sad, on a windy day it's angry, on a sunny day, it's happy, and early in the morning it's calm.
When asked what I mean by these things: are those the emotions that I feel, I would say, no, they are the nature's qualities. I can feel such emotions myself, but in this case, I am describing the states of nature. Well, do I mean that the nature feels those emotions? No, that's silly. I am just describing the nature's properties or some truths about nature, and no further definition is necessary. How do I know that the nature has these states? Why, I observe it. I already know what angry, happy, sad, or calm are from introspection. I can also recognize these qualities in nature. There are those that can agree with me, and there are those that cannot sense those qualities in nature; maybe they are psychopaths of sorts.
I think most people would find these descriptions not only somewhat silly, strange, and arbitrary, but also not very useful.
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So, how do I personally define objective valuations? First, I want to return to the idea that a valuation is an expression of correspondence to some goal. Something is good if it allows one to reach some goal.
The goal itself may or may not need justification; it may or may not need be a part of another goal. For instance, I eat because I don't want to be hungry and want to survive. I don't want to be hungry because I don't want to suffer. My goals of not suffering and continuing to survive cannot be explained; they are what defines me as who I am.
Perhaps the latter point needs some work. Maybe it is wrong to define something as an end in itself or an axiom without a good justification. (Such that denying it would force one to contradict oneself, such as saying "I don't exist".) I do not know yet if one can apply this method to goals to verify which of them are "basic" (or "final") goals.
Be it as it may, let me quote myself from an earlier post:
How can there be an absolute, "objective" purpose to the world out there? I walk in a forest and see a beehive. My purpose for it is to eat the honey to satisfy my hunger. The bees' purpose is to keep the honey to feed their larvae. Maybe somebody else's purpose is to take the honey and sell it on the market. How can there be an "ultimate" or absolute purpose, independent of any agents, built-in into the fabric of reality of the beehive?
Clearly there cannot be, unless there is one agent who imbues all reality with a purpose: the one who created and continues to create the beehive, consciously, willfully, and with a certain goal in mind (so to speak). I.e., G-d, [the Creator of the World, imbuing it with a purpose].That is my definition of objective morality. It is that which corresponds with the objective, teleological end of the world, its purpose. Those who don't believe in G-d might believe in something like Omega Point theory, which states that the universe has a teleological purpose defined in its laws to which it tends. In that case, following that purpose is good, while going against it is bad.
I am not making this definition because I am trying to fit morality into religion. Simply all the other definitions do not make any sense to me. (And subjectivist morality contradicts my perception of intuitive, non-subjective truths being real.) I may change my mind, but this is where my view stands at the moment.
Finally, I do not mean to say that the only way to know G-d's purpose for the world is through a revelation. Another way is, potentially, through intuition, one's "moral compass". It may or may not be a good way to know G-d's purpose in certain things, just like our eyes may or may not be a good way to gain knowledge about space, time, colors, etc.
I think one's moral landscape must consist of a symbiosis between one's knowledge of G-d's revelation of His desires about the world and one's moral intuition.