Why objective moral facts would be the strangest things in the universe
In 1977, philosopher J. L. Mackie argued that all objective moral claims are strictly false. His "argument from queerness" noted that if objective values existed, they would be fundamentally unlike anything else in nature: physical properties that somehow carry an intrinsic, built-in demand telling conscious beings how to act. To perceive such supernatural moral properties, humans would require a mysterious, magical sixth sense. Because no such queer entities exist, morality is entirely an invented human framework.
The Error Theory of Everyday Morality
In 1977, the Australian philosopher J. L. Mackie published a foundational challenge to traditional ethics in his book 'Ethics: Inventing Right and Wrong'. Mackie began with an uncompromising assertion: there are no objective values. This position, known in philosophy as moral error theory, does not claim that moral language is meaningless or purely emotional. Instead, Mackie accepted that ordinary moral discourse is fully cognitivist—meaning that when people say 'stealing is wrong' or 'courage is good,' they intend to state factual claims about how the universe actually is. However, Mackie argued that because the universe contains no objective moral facts whatsoever, every positive moral claim is systematically false.
To illustrate how an entire category of language could be systematically mistaken, philosophers often draw comparisons to beliefs about witches or the historical theory of phlogiston. In earlier centuries, people used the word 'witch' intending to refer to human beings possessing supernatural, malevolent powers. While the term was meaningful and people made declarative assertions using it, the world contains no persons with supernatural witchcraft powers; consequently, all positive claims identifying specific individuals as witches were false. Mackie argued that objective moral concepts suffer the same fate. Society operates as if objective values are real features of the external world, yet this assumption rests on an unexamined, pervasive error.
The first half of Mackie's central critique is the metaphysical argument from queerness. Mackie observed that if objective moral values did exist, they would have to be entities, relations, or qualities of a profoundly strange sort, utterly unlike anything else found anywhere in the natural universe. Science describes physical properties like mass, electric charge, shape, and velocity. These properties tell us what exists, how things interact, and what causes what, but none of them come equipped with an automatic directive instructing an agent on how they must act.
An objective moral property, by contrast, would have to possess what Mackie described as an intrinsic 'to-be-pursuedness' or 'to-be-avoidedness' built directly into its fabric. If a state of affairs possessed objective goodness, it would not merely exist; it would inherently exert an objective pull, placing an authoritative demand on any conscious agent who encountered it, completely independent of their personal desires, psychological inclinations, or cultural conditioning. Mackie pointed to Plato's Forms as the historical archetype of this idea, where knowing the Form of the Good supposedly compels the knower to act rightly. In a natural world governed by physics and biology, a property that intrinsically commands obedience simply by existing is, metaphysically speaking, entirely queer.
Epistemological Queerness and the Moral Sixth Sense
The second branch of Mackie's argument addresses epistemology: the question of how human beings could ever come to know such objective moral properties if they were real. Humans acquire knowledge about the world through familiar empirical means—such as sensory perception, tactile interaction, introspection, and rational inference based on observation. We observe light hitting an object, track heat through nerve endings, or infer the existence of unobservable particles through their measurable causal effects on physical instruments.
None of these standard epistemic mechanisms can detect a non-natural, prescriptive moral value. Seeing an act of violence allows us to observe physical movement, hear sounds, and register emotional distress, but the non-physical property of 'objective badness' cannot be viewed under a microscope or detected by a sensor. Mackie argued that to perceive such values, human beings would need an entirely mysterious faculty of moral intuition—a kind of metaphysical sixth sense. Because early twentieth-century intuitionist philosophers like G. E. Moore never provided a coherent causal explanation for how this intuitive faculty interacts with non-natural qualities, Mackie concluded that positing an unexplainable perceptual organ was an ad hoc evasion rather than a credible epistemology.
The Insoluble Riddle of Supervenience
Mackie's argument from queerness extends into the puzzle of how moral qualities are supposed to relate to ordinary natural facts, a relationship modern philosophers call supervenience. In moral discourse, people invariably ground their moral judgments in physical realities. If someone is told that an action is wrong, they naturally ask what features of the action make it wrong. The answer will typically point to physical facts: the action involved deliberate deception, inflicted bodily suffering, or broke a contract.
Mackie asked what kind of metaphysical connection could possibly bind the physical act to the non-physical moral property. What constitutes the bridge between the descriptive fact that an act causes pain and the prescriptive fact that it has an objective property of wrongness? It is not an ordinary causal link, nor is it a simple logical identity, since pain is a physiological state whereas wrongness is a normative demand. Mackie contended that moral realists had never successfully explained how natural properties generate, support, or link to these non-natural values, leaving the connection just as baffling as the properties themselves.
Companions in Guilt and Naturalist Pushback
Philosophers who defend moral realism have developed several distinct lines of response against the argument from queerness. One prominent defense is the 'companions in guilt' argument. This view points out that morality is far from the only domain that relies on entities or standards that do not fit neatly into a physicalist ontology. Mathematical truths, logical necessities, and even the normative standards of epistemic rationality itself—such as the requirement that one ought to believe what the evidence supports—are neither physical objects nor detectable with physical sensors. If Mackie's argument proves that non-empirical, normative truths cannot exist, defenders argue it might also threaten mathematics, logic, and scientific reasoning.
Another major counterattack comes from moral naturalists, such as the Cornell realists, who reject the claim that moral properties must be non-natural or weird. These thinkers argue that moral properties like goodness or justice are complex natural properties, closely tied to human flourishing, social cooperation, and psychological well-being. From this perspective, morality does not require supernatural entities or a magical sixth sense; moral facts are simply higher-level natural facts about human social systems, comparable to concepts in sociology, economics, or evolutionary biology, which describe real conditions without invoking cosmic prescriptions.
Projectivism and Life Without Objective Facts
If objective moral facts do not exist, a critical question remains: why do people around the world persistently believe that they do? Mackie answered this through a psychological theory known as projectivism, heavily influenced by the eighteenth-century philosopher David Hume. Human beings experience internal emotional responses—feelings of empathy, disgust, indignation, or admiration—and systematically project those subjective sentiments outward onto the external actions that triggered them. Over generations, these projected attitudes become reified, creating the persistent illusion that values are inherent in the objects of our judgment rather than products of our internal psychology.
The recognition that morality is an invented social framework rather than an objective reality does not necessarily lead to the abandonment of moral rules. While error theory establishes that moral properties do not inhabit the universe as external furniture, it leaves room for positions like moral fictionalism. Fictionalists argue that even if moral claims are strictly false, adopting moral discourse as a useful fiction remains indispensable for resolving human conflicts, facilitating mutual coordination, and promoting peaceful coexistence. In this view, morality is not a discovery of cosmic law, but an exceptionally practical human tool.
Key takeaways
•J. L. Mackie's moral error theory holds that everyday moral discourse makes factual claims, but because objective moral properties do not exist, all positive moral assertions are systematically false.
•The metaphysical argument from queerness states that objective values would require an impossible feature: intrinsic, built-in prescriptive demands that objectively compel human action regardless of personal desires.
•The epistemological argument from queerness shows that discovering non-natural moral facts would require a mysterious, inexplicable faculty of intuition fundamentally unlike any known human sense.
•Mackie explained the widespread belief in objective morality as psychological projection, where internal emotional reactions are mistakenly assumed to be external qualities of the world.