The Humean-Platonic tripartite (Ought-Is-Belief) theory of (moral) knowledge

The Humean-Platonic tripartite (Ought-Is-Belief) theory of (moral) knowledge
It is possible to blend Hume’s is-ought distinction (1) in Ethics with Plato’s justified-true-belief theory of knowledge. 

Simply put, whatever sort of beliefs one is talking about, including moral beliefs, they must be ‘both’ justified by reasons (a justified belief OUGHT to be believed) ‘and’ correspondent to reality (a true belief IS true). Just because one has good reasons for one’s belief does not mean it is true. And even if one believes something that is true, one may have horrible reasons for believing it (bit of a tangent: Gettier was wrong in assuming falsehoods count towards justification) (Gettier is answered elsewhere (2)). All of this is true about any belief one holds, moral or otherwise. In order for one’s belief to be knowledge, it must satisfy those two conditions: 1: It must be backed by good reasons (justified/ought). 2: It must correspond to reality (true/is). These conditions are very different from each other. Both are required separately. So, satisfying both conditions is not Hume’s problem—it is when one condition takes the place of the other that one commits Hume’s is-ought fallacy, or its reverse (ought-is).

That said…

Hume obviously only drew this distinction when he was discussing moral knowledge, not any other kind of knowledge, and Plato grappled with Euthyphro’s (false) dilemma (it, skeptics, anti-realists and Gettier are all answered elsewhere (2)).

If one understands the blending and one is not a Christian, one may not be comfortable with it because one’s moral theory doesn’t correspond to, or describe, anything in reality, knowing of no always-good person who never has and never will violate one’s moral theory. That discomfort, though understandable, is not a valid reason to reject the is-ought distinction.

If one is a theist who still rejects Hume’s is-ought distinction because one thinks it means the Good cannot correspond to God, then one is misunderstanding what Hume really meant by his distinction, and there is still some work to do in communicating the blending properly. Even educated Christians like Dr. Richard Weikart and Dr. William Lane Craig share such a misunderstanding. Dr. Craig says:

(quotes omitted) …the theistic view is that these qualities are good because (Maryann: rather than exist as, or exist if) they are found in God’s nature. The alternative (that God is good because his nature matches the Good) is just Platonism all over again, which we’ve already rejected (see my three-pronged critique of Platonism).



The theory that I have defended is a form of Divine Command Theory. According to this view our moral duties are constituted by the commands of an essentially just and loving God. It seems to me that this theory does derive an “ought” from an “is,” and justifiably so—though not in the way you imagine. The theory does, as you say, ground moral values in God’s unchanging nature. God is the paradigm of goodness. But that is not to say that “because God is a certain way we ought to behave in certain ways.” No, our moral obligations and prohibitions arise as a result of God’s commands to us. God’s nature serves to establish values—goodness and badness—while God’s commands establish moral duties—what we ought or ought not to do. Grounding moral values in God no more derives an “ought” from an “is” than does Plato’s grounding values in the form of the Good (indeed, one of my critiques of moral platonism is precisely its failure to provide any basis for moral duty). The theist and Plato just have a different ontological ultimate.


It is unclear here whether or not Dr. Craig thinks the is-ought fallacy is a real fallacy. He seems to when he dismisses the idea that “because God is a certain way we ought to behave in certain ways” (ibid). But he seems not to when he asserts “our moral obligations and prohibitions arise as a result of God’s commands to us” (ibid). It is a tangent, but he also unnecessarily distinguishes between moral obligations and moral values. Anyway, to say “because this is God’s command, we ought to behave according to it” commits the is-ought fallacy.

There has been some discourse with Dr. Craig on this matter via Facebook (5), and via email with Dr. Weikart. Dr. Weikart’s most recent reply just restates his misunderstanding: 

You are denying the is-ought distinction, because (Maryann: according to me, Maryann) moral goodness (ought) is integrally connected to God’s being (is).

(via email)

Grounded in, yes. Justified by, no.

Reference List

1. Ichthus77. (2011). Where I am at with Hume’s is-ought distinction. Retrieved from

2. Ichthus77. (2011). Answering Gettier. Retrieved from

3. Reasonable Faith. (2012). Moral Argument for God. Retrieved from

4. Reasonable Faith. (2012). Does Theistic Ethics Derive an “Ought” from an “Is”? Retrieved from

5. Ichthus77. (2012). Is-ought discussion with WLC. Retrieved from 

This entry was posted in Euthyphro Dilemma, Gettier Problem, Is-Ought Fallacy, Justified True Belief, William Lane Craig. Bookmark the permalink.

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