An Argument From Nature for Moral Realism

Why should we think moral facts exist and moral relativism / nihilism is false? Here’s a metaphysical argument from nature that I really like because it doesn’t depend on intuition:

  1. If there are rational agents with natural goods then moral goods exist.
  2. There are rational agents with natural goods.
  3. Therefore, moral goods exist.


The basic claim is that moral goods must exist if a rational agent with natural goods exist. First, let’s define our terms. A natural good is a good that is determined by what fulfills a thing’s nature. For example, rich soil is good for a tree and dry sand is not. This is determined by the tree’s nature; whereas something with a different nature may be fulfilled by sand as opposed to rich soil. Another example is a man born blind. By virtue of having a human nature, he should have eyesight; recognizing this fact is why we recognize blindness to be a defect. We call what is proper to nature a natural oughtness. A moral good by contrast specifically refers to a good that a rational agent ought to will for oneself and others — what that good precisely is will be covered next.

With that clarification, I’ll defend premise (1) and (2). It is obvious that there exist rational agents with natural goods; they’re called human beings. Eating apples for us is a natural good, whereas drinking battery acid is contrary to our good. How then do we go from natural goods to moral goods? Well, a moral good is just a special instance of the natural good, but in particular it’s the natural good of an intellect and a will. What is the intellect’s natural good? To know and understand what is true and good. What is the natural good of the will? To freely will what the intellect presents as truly good. Together they naturally produce a unique power called responsibility.

It is this power added to a natural good that transforms a mere natural good to a moral good. In other words, morality is just being responsible (or culpable) for willing natural goods within one’s control. We can refine our definition of moral good as “a natural good that a rational agent ought to will for oneself and others.” This natural good is an ought that applies to you whether you will it or not because it derives out of your nature. It is not some external ought imposed upon you which allows you to ask, “Why should I care to act morally?” but is instead an ought that exists in the very structure of human existence. You cannot help but will or not will in accordance to this natural obligation, which means you cannot help but be a moral agent.

Here are three reasons why it is plausible to identify morality with natural goods: (i) It is impossible to have a moral good that’s wholly detached from a natural good. Unless we want to make morality wholly arbitrary, they must be grounded in nature. Just try to think of a moral good that has no relevance whatsoever to nature. I’ll wait. (ii) This view has more explanatory power as it explains why moral obligations only applies to rational beings with a capacity for being responsible — an assumption that most ethicists simply take for granted — and makes far better sense of where moral goods come from. (iii) All morality in principle involves exercising our reason and will in accordance to a natural good, so this meta-ethical view is really impossible to avoid regardless of your normative theory of ethics.


Someone might object, “But how do you go from a natural ought to a moral ought?” You don’t. The “moral” ought is just a natural ought applied to a person capable of being responsible for their actions. There’s no is-to-ought gap (or naturalistic fallacy) as Hume and other modernists held. There’s only a gap if we said non-rational beings had moral obligations.

Another may just deny (2) altogether and bite the bullet. In which case it’s difficult to convince a person who wants to deny something as obvious as natural goods. You often cannot reason someone out of their irrationality; it’s like trying to use water to rescue a drowning person. There seems to be a cognitive dissonance as well. If this same nihilist gets a heart attack, they will often recognize it as bad and desire to repair the heart to what it naturally ought to be despite denying belief in natural goods. But as a sort of last ditch effort to persuade the nihilist, I would point out that their request for a justification of premise (2) already assumes that justifying our beliefs is naturally good for us.

Lastly, someone could just do some foot-stomping and insist that this natural good view of morality is just not what morality is. Sorry, but if you define morality as not grounded in nature, then all you’ve done is define yourself into victory in order to protect moral anti-realism.


The question to ask yourself is what view makes the most sense of reality and the natural behavior of human beings. All of us act as if moral facts exist in the same way that we act as if other minds, causality, or an external world exists. Realism is a package deal; if you reject one you reject the other because we often use the same common sense reasoning to accept them. You can provide special pleading exceptions of course, or be convinced that you have good reason for making an exception for belief in external minds but not moral facts, but the fact remains that we are naturally built to treat such beliefs with nearly equal force.

However, for those who are not convinced of the common sense + slippery slope argument, I have developed this metaphysical argument. It goes without saying that a lot more can be said than what I have been able to write in this blog post. Please do not hesitate to share your thoughts!

1 thought on “An Argument From Nature for Moral Realism”

  1. Excellent argument. This reminds me of Dr. Feser’s spin on Kant’s categorical imperative, that is, if you want what is good for you, then you must act in such and such a way.

Leave a Reply

Your email address will not be published. Required fields are marked *