The way we usually speak, shows this. We constantly claim things to be right or wrong, as if those are facts about the world that we come to know about through our conscience. We could swear that such facts are true and that they transcend us and bind us, but shouldn't we demand evidence for the existence of such things or is our intuition enough?
Is our intuition enough?
I don't think there are any other reasons to think that morality is objective apart from our intuition, but is that a good reason alone? Our intuition has been shown to be a great aid in survival but it just wasn't meant to be used as an arbiter of truth. It has been shown to be wrong many times in the past.
It's also something that should not be ignored automatically though, if there's no way to confirm or deny our intuition then we would be reasonable in presuming it to be true. However, that's a very weak assumption that shouldn't be held against a conclusion that follows from your world-view. So is there anything else supporting an objective morality besides our intuition?
Stealing is wrong because it's unfair. Torture is wrong because it causes pain and suffering. These are objective grounds for moral judgment.
An objection that can be raised is that we can use reason instead of just our conscience, to determine the moral course of action. If we could, then our judgments of moral action would become objective:
- For example, we can act in accordance with a general principle that specifies that whatever maximizes happiness and reduces suffering to most people is the moral action. For example, torture might be morally justified, even at a risk of torturing innocents, if thousands of lives are at stake; lying may be the right thing to do to someone to avoid needless suffering (imagine a woman in the last moments of her life and you just receive the news that her son was killed).
- Or maybe we could argue that moral action stems from a number of duties that must be followed regardless of the consequences. In this case, telling the truth may always be the moral action, regardless of the amount of suffering it provokes. Honoring your promises and commitments may be the right thing to do even if it will lead to negative consequences for yourself or for others.
In other words, if you ground your moral action in the moral system of your choice, where do you ground the moral system itself?
On the other hand...
It seems to me that intuition is indeed the only thing supporting objective moral value but as I said before, it may be enough for us to reasonably have that belief if there's no reason to deny it. So, is there any reason to deny it?
Grounding objective moral value in the natural world.
One good reason is that natural sciences can't seem to provide warrant for that belief, which has traditionally led to positing the existence of objective moral value in a supernatural world instead. On the other hand, it's trivial for science to root a subjective morality in the natural world so, if our world-view doesn't account for the existence of a supernatural world, then I can't see where this objective morality would reside.
The keyword "ought".
Moral judgments refer to a comparison between what a thing is and what a thing ought to be, as if there is a state that we're aiming for and that we try to approximate. For morality to be objective, reality needs to encompass both what is and what ought to be. However, statements about what ought to be are never properly justified when they're made and the reason why they're never justified is probably because they are impossible to justify which points to a subjective nature of such claims as I explain below.
Can you prove that torture is wrong?
There's one thing that all subjective phenomena have in common, it's the impossibility to prove or show them to another person. Imagine a painting that you find beautiful, now what if I don't like it, how could you show me that I'm wrong and that the picture is truly beautiful? The same could be said about taste, I love chocolate but I know there must be someone out there who doesn't. How could I prove that I'm right when I defend that chocolate is indeed, delicious?
I couldn't prove neither of both claims, in fact, I couldn't even argue for them in a meaningful manner and that's because it doesn't make sense to talk about subjective phenomena as if they're objective features of the world. Since these things depend on the subjects, putting them in sentences as if they depend on the objects will lead to contradictions. For example, "chocolate is delicious" can't be true nor false because deliciousness is not a property of the chocolate. Of course that, in our everyday language, we use such statements but we usually mean something else than the literal meaning, like "I find chocolate delicious" or "the majority of people finds chocolate delicious", which are valid statements because they relate to the subjects instead.
I think there's a strong parallelism between our observations of ethics and these subjective phenomena but to show that, let's try to prove a moral claim. How could you prove that torturing someone for fun is wrong? You could argue that it is wrong because it causes needless suffering but then, why is causing needless suffering wrong? Maybe because that's the best moral principle among all the alternatives... but "best" in what respect exactly? What criteria can be used to judge how "good" a moral system is and to differentiate between them? Who chose that specific criteria and why that criteria and not any other?
If we don't stop too soon in our search for answers, I believe that we'll find it impossible to arrive to an objective answer, it's almost as if we're asking the wrong question, as if the statement about what ought to be is invalid and doesn't even make sense to be asked. This is a very consistent result with other subjective phenomena.
To sum it up...
I must admit that this isn't definitive proof of a subjective morality. In order for that to happen, we'd need to conclude that the impossibility to arrive to an answer is in fact of a metaphysical kind, as opposed to a physical impossibility. For example, it may be impossible to know the color of a dinosaur's skin but this is merely a physical impossibility. The information is gone in the past but the question is still valid, it still makes sense to be asked. A metaphysical impossibility would be for me to show you the beauty of a painting. I can only show you the painting itself and maybe some reasons for you to appreciate it but I can't show you its beauty because the nature of what beauty is doesn't allow it to be shown.
Even though I believe that this impossibility is indeed, of a metaphysical kind, I can't see a way to climb that very last step using deductive reasoning, but even though we can't arrive at an answer with absolute certainty, I believe that we can arrive at what I think is the overwhelmingly most likely answer to this question. So, based on the assumption of a naturalistic world-view, the lack of arguments for the case of objective moral value, the inability to ground what ought to be in reality, the ease of explaining subjective morality in reality and the analogy with other subjective phenomena, I believe that we would be much more reasonable to presume morality to be subjective.