Updated: Jul 7, 2020
One of the strongest arguments against unbelief is the argument from morality. It shows that, if God doesn’t exist, we cannot reasonably expect anyone to adhere to any moral laws. It shows that without God, moral values and duties are ultimately meaningless. It shows that no atheist can expect anyone to adhere to any sort of morality without betraying his own most basic presuppositions. After all, who says I shouldn’t torture kids in my basement – your grandma?
Central to this argument is Hume’s is-ought problem. The is-ought problem shows that we cannot derive an ought from an is. We cannot derive “you shouldn’t torture” from “torture hurts people,” or even “torture is evil.” In simplest terms, amoral facts are just that: amoral. They don’t prescribe, they simply are. No moral obligation can be inferred from them.
Moral values and moral duties
It’s important at this point to differentiate between moral values and moral duties. Moral values pertain to what constitutes goodness and evilness. Moral duties pertain to what we ought and ought not to do. Moral values describe states as either good or evil, right or wrong, while moral duties obligate us to do that which is good and right.
Think about it like this. Let’s assume that an objective standard exists by which we can measure all states and actions and describe them as good or evil. This standard in and of itself doesn’t require us to do anything. It doesn’t obligate us to do things that are good, and not do things that are bad. It simply determines whether what we do is good or bad. This is where moral duties come into play. Moral duties require, prescribe, and obligate us to do certain things. More accurately: moral duties require us to do that which is determined to be good by the moral standard. So we need both objective moral values and objective moral duties to answer the question “how should we then live?” 
The is-ought problem and Christianity
The is-ought problem is crucial to almost all moral arguments. And because it’s so simple it’s also very effective: anyone with more than two brain cells can see the truth of it. Because of the is-ought problem, many atheists will even acknowledge that their worldviews cannot explain objective moral duties. They don’t live, speak, write, or argue like this is the case, but they’ll acknowledge it.
However, the same argument is frequently pressed on Christianity as well. The question is asked whether we (Christians) can account for moral duty. This is fair: we shouldn’t criticize atheism for poking holes in the air if we cannot justify moral duties ourselves.
The argument goes that, though Christians can account for objective moral values (what is right and wrong) we cannot account for moral duties (what we ought and ought not to do). It is important to note that the argument is not presented against moral values. Rather, it's presented against moral duties. Many atheists will readily acknowledge that Christians can objectively distinguish between goodness and evilness by comparing it to God’s nature (absolute goodness). But they argue that we cannot justify moral obligation without deriving an ought from an is (i.e we ought to love because God is love).
The obvious response to this argument seems to be that we don’t derive moral duties from God’s nature, but rather from his commands. We shouldn’t rape, not only because it’s against his nature but because He commands us not to rape. To this, the skeptic retorts: “But why should we obey his commands?” This is a really good question. Why should we obey God’s commands? Do they naturally inflict obligation? How can we justify that they do? I mean, after all, Joe from downtown can command all he wants, I have no obligation to follow his commands. So what makes God’s commands different? Should we obey them simply because He’s omnipotent? But isn’t this just another version of “might makes right”? What’s the difference between us saying we should follow God’s commandments and the atheist saying we should follow the laws set out by the majority?
We must admit that this argument is very strong – especially since we’re usually so skeptical about the atheist’s attempts to justify objective moral duties. Is it not clear that our own worldview crumbles under the very weight we constantly expect atheism to bear (and criticize for failing to do so)? This is the question I’m attempting to answer in this article (spoiler: Christianity can support moral duties).
Answering questions from our worldview.
Before we proceed, it’s important to realize that we, as Christians, should answer objections raised against the Christian worldview from the Christian worldview itself. This just makes sense: when we’re presented with arguments against the Trinity, we should respond by using the Bible to establish what we mean when we declare that we believe in a Triune God. Attempting to get a definition for the Trinity from anywhere else would be madness!
Scott Oliphint, while discussing the problem of evil, writes :
Since the objector presents the problem as one intrinsic to Christianity, there is no fallacy or logical breach if one answers the objection from the same source in which the alleged problem itself, including the characteristics of God, is found.
This is important: since the is-ought problem is here presented as an inconsistency in our worldview (and as such assumes the basic claims of our worldview for argument’s sake), our solution may (and should) come from the same source as the problem. We have no obligation to answer the objection by appealing to mutually agreed-upon principles. As such, we can (and should) appeal to our entire Christian worldview regulated by Biblical principles. The unbeliever may object that he doesn’t believe that the Bible is true, but that holds no bearing on the validity of the solution. The problem is presented as an inconsistency within the Christian worldview. Hence, our solution shall also come from the Christian worldview.
A question of epistemology.
Since we’ve established that our answer should be from our worldview, let us discuss our epistemology. If you’ve never heard the word before, epistemology is the study of knowledge. In simplest terms it attempts to answer two questions: (1) “what do we know?” and (2) “how do we know what we know?” Of course, as Christians, our epistemology will be radically different from an atheistic epistemology – as different as day is from night. Some Christians disagree with the claim that the Christian epistemology is different from an unbelieving epistemology, but that’s material for another article.
For this article, we’re mostly interested in the second question epistemology attempts to answer: “how do we know what we know?” It’s important to realize that we disagree with atheists on this question. Atheists will answer that we know something is true, either because of rational argument or empirical evidence (proofs). Though we agree with atheists on the usefulness of rational arguments and empirical evidence, we don’t agree that they’re the ultimate standard for knowledge. Our epistemology stands not on the frail pillars of human thought and our limited capacity for observing the world. Our epistemology ultimately rests in the Word of God. This distinction is of paramount importance.
But how does this affect the claim that Christianity cannot account for moral duties? Allow me to explain: the claim that Christianity cannot account for moral duties is epistemological in nature. It pertains to what we can know.  If we assume an unbelieving epistemology, what naturally follows is that moral duties are impossible (in the sense that they cannot be derived from anything we know). This makes sense: neither rational thought nor empirical facts are moral in nature. If all things we know are knowledge by virtue of rational argument and empirical fact, everything we know is amoral!
This is where we must challenge the unbeliever’s assumption: do we (Christians) really ascribe to an epistemology of rationality? Of course not! Though we value rationality (by virtue of being from God) it’s not the foundation of our epistemology. It’s not the ultimate standard by which we judge knowledge. God’s Word is. It is important that we make this distinction: we don’t believe all knowledge boils down to empirical facts and rational truths. God’s Word is the ultimate standard for knowledge, and because of this, we can know truths that aren’t rational or empirical. We can know truths that are moral.
Moreover, we can know moral duties. When God commands us to do certain things, the command itself obligates. In this sense, it’s not merely a static fact that God commands (though it certainly is), but his very commands obligate and demand obedience. Moral duties are not derived from his commands, his commands are moral duties. We’re reaching the descriptive limits of the English language, but allow me to say this: the knowledge of God’s commands is not static. The knowledge of his commands is incomplete unless obeyed. In this sense, his commands are both static and dynamic (or prescriptive). We can only know his commands in this dynamic sense if we obey them. To obey, then, is to know.
Because we have this different epistemology, we Christians have an entirely different view of reality. Unbelievers have to conclude that there aren’t such things as moral truths (or at least, that we cannot know them) because their epistemology doesn’t allow for these truths to be known. Moreover, because all rational and empirical truths are static, any duty (whether moral or not) must ultimately be a derivation. But because God’s Word is not simply rational and empirical (and definitely not static), we can know moral values and moral duties. When we look at reality we see moral values (rape is evil) and moral duties (we shouldn’t rape), because our epistemology demands these things to be true.
The nature of God’s Word, and how it affects epistemology
This may sound complicated, and even sketchy at first hearing, so allow me to give you another perspective on why I don’t think the is-ought problem is really a problem for Christianity.
Since we’ve established that God’s Word is the ultimate standard for knowledge, we need to discuss the nature of his Word. What sorts of things are in the Bible? And what does it mean for these things to be the starting point of our epistemology? We can’t get into all the different aspects of the Bible, but I want to focus your attention on one aspect of God’s Word: his commands. God’s Word contains commands. This should lead us to ask the following question: what does it mean to know a command? Because his Word is the foundation of our philosophy of knowledge, his commands play a role in what we know. But what does it mean to know “you shall not steal”?
Well, two senses of knowing come to mind: a static sense and a dynamic sense. To know a command in a static sense is to know simply of the command: to know that there is a command. But to know a command in a dynamic sense is to not only know that there is a command but also to obey said command. Hence, to obey is to know.
Let’s consider “you shall not steal” once more. Do we know this command if we simply know that God commands us not to steal? Certainly not! The Bible most definitely doesn’t teach that knowledge of God’s commands is an abstract thing: to know simply that there is such a command. The knowledge of God’s commands is more significant than mere knowledge of the fact that He commands. To know God’s commands fully is to know both that He commands and to follow said command. As such, we don’t derive moral duty from his commands, his commands themselves inflict moral duty. In a sense, they are our moral duty, because we cannot know them fully unless we obey them. To know the 8th commandment, then, is to not only know of it but to do it.
Greg Bahnsen alluded to this point in Van Til’s Apologetics: “The question of knowledge is an ethical question at the root. It is indeed possible to have theoretically correct knowledge about God without loving God. The devil illustrates this point. Yet what is meant by knowing God in Scripture is knowing and loving God: this is true knowledge of God: the other is false.”  Bahnsen is writing here specifically about knowing God. But the same can be said for knowing his commandments. One can know what God commands without knowing his commands at all! True knowledge of God’s commands is knowledge of and obedience to his commands.
Ethics, truth, and the Scriptures
We find this same idea (moral duty being connected with knowledge and truth) in the Bible. Let’s take Ps. 26:3:
For thy lovingkindness is before mine eyes: and I have walked in thy truth.
David here uses the word truth. This doesn’t conflict with what we’ve previously established: moral duties being a form of knowledge. Greg Bahnsen notes that “instances of knowing are instances of believing, but one can know a proposition only if it’s true.”  So then, we can say that to be ethical, is to know God. To “walk in God’s truth” as David put it.
We can also look at John. 3:21:
But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God.
In this verse, Jesus is actually claiming that to do good is to do truth! To obey God’s prescriptions is equivalent to doing truth. This should have a huge bearing on how we view ethics and epistemology.
Finally, we see the same thing once more in 2 John 1:4:
I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father.
Here John writes to this mysterious figure he simply refers to as “the elect lady,” and he writes that he rejoiced because her children were “walking in truth.” Walking in this sense is almost always used to refer to someone’s life: to establish whether they’re living morally. John even makes this clear in the second half of the verse: “as we have received a commandment from the Father.” (Emphasis added). John is equivocating walking in God’s commandments to walking in truth.
Let’s use an example
Allow me to make all of this more concrete by providing an example. Let’s take the 6th commandment: you shall not murder. The question is asked: why should we obey this command? If we assume an epistemology of rationality, it seems absurd to suggest that we ought to obey this command because of two reasons: (1) all knowledge is rational, and we cannot derive something that is moral from something that is rational; (2) all knowledge is (ultimately) static (because it’s rational) and no non-prescriptive fact infers duty.  To be clear, atheists can know commands (I’m sure they here them just as frequently from their parents as you and I) but an atheistic epistemology doesn’t allow for these to be authoritative, because all true knowledge (in atheism) boils down to rationality (which isn’t prescriptive in any sense).
But the picture changes quite a bit when we presuppose an epistemology based on God’s Word instead of rational thought. God’s Word doesn’t limit knowledge to the rational. Hence, because our epistemology is based on God’s Word instead of rationality and both issues arises because atheistic epistemology is based on rationality, both issues are nonexistent in the Christian Worldview. God’s Word is more than rational. His Word is also moral, and dynamic. It allows for truths to be moral and prescriptive. And because these truths form part of our epistemology, to obey them is to know them fully.
A few concluding thoughts
The Christian worldview is drastically different from an unbelieving worldview. Especially when we consider morality we notice how much our worldview differs from the worldview of those who deny the existence of God. Christianity grounds moral values firmly in God’s nature, and moral duties firmly in his commands. But atheism is left without any means to objectively ground either moral values or duties.
We should ask ourselves why we don’t see such a drastic difference between the lives of atheists and Christians if our worldviews differ so much. Why do we see virtuous atheists and immoral Christians? This is a necessary question in our day. And the answer takes us back to Genesis 1-3. Though we have different worldviews, we’re all made in God’s image and we’re all born in sin because of the Fall. All humans share these two truths: we were created good, born bad. And because we share these two truths, in many ways, Christians and unbelievers are alike.
But by God’s grace, for some of us there’s another truth. The truth of Jesus Christ – the God-Man. The Redeemer promised in Genesis 3:15. He is called “God with us!” (Isa. 7:14). He calls Himself “the way, and the truth, and the life.” (John. 14:6). “In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace.” (Eph. 1:7).
Jesus is the ultimate difference between believers and unbelievers. Only through God’s grace shown in Jesus are we saved. Let us remember this, and not be proud. Let us remember this and work all the more for God’s glory: always ready to spend and be spent for God’s kingdom; always ready to fight when we’re called to fight, and die when we’re called to die. And whether we live or die, let our prayer be: pro Rege – for the King!
 Francis Schaeffer has written a great book with this very title. I’d recommend it to anyone as an introduction to the Christian worldview within its historical context.
 Scott Oliphint, Covenantal Apologetics.
 I’m not dismissing the ontological aspect of the claim. The claim is also ontological in nature, but for the sake of brevity, I will not be getting into that in any detail in this article. In this article, we’re mostly interested in the epistemological aspect of the claim.
 Greg Bahnsen, Van Til’s Apologetics.
 Greg Bahnsen, Van Til’s Apologetics.
 We don’t derive any duty from our existence (which is the starting point of modern unbelieving philosophy). This is because rational knowledge (flowing from an epistemology of rationalism) isn’t prescriptive, meaning it isn’t dynamic.