When we ask why something is the case, we might be asking two very different questions. Why did the window shatter? Because the rock struck it—a causal explanation tracking events through time. But why is the act of torturing innocents wrong? Not because some earlier event made it so. Its wrongness is constituted by features it possesses right now. This is a metaphysical explanation, and it operates on entirely different principles.

Philosophy has long recognized that not all explanation is causal. Yet the distinction between causal and metaphysical explanation has only recently received the rigorous, systematic treatment it demands. The result is a richer picture of explanatory structure—one where reality has both a horizontal dimension (how things unfold across time) and a vertical dimension (how things are built up from more fundamental facts at a time).

Getting clear on this distinction matters far beyond academic taxonomy. It reshapes how we understand dependence, determination, and the architecture of reality itself. If we collapse metaphysical explanation into causal explanation, we lose the conceptual resources needed to articulate the layered structure of the world.

Causal explanation has a distinctive temporal signature. Causes precede or are simultaneous with their effects, and causal chains stretch across time. When we explain why the bridge collapsed, we trace a sequence: corrosion weakened the supports, stress accumulated, structural failure followed. The explanatory arrow points forward through time—from earlier states to later states. This is the diachronic, horizontal dimension of explanation.

Metaphysical explanation operates on a fundamentally different axis. When we explain why a particular set is a singleton—say, {Socrates}—by citing the existence of Socrates, we are not pointing to anything earlier in time. Socrates and {Socrates} exist simultaneously. The explanation runs from what is more fundamental to what is less fundamental, not from what is temporally prior to what is temporally posterior. This is the synchronic, vertical dimension.

The structural difference here is not merely one of direction but of the very geometry of explanation. Causal explanation maps the world as a process—a river of events flowing from past to future. Metaphysical explanation maps the world as a hierarchy—a layered edifice where some facts constitute or ground other facts. A mental state obtains in virtue of a neural configuration. A legal fact obtains in virtue of social practices and institutional arrangements. In none of these cases does temporal precedence do the relevant work.

This distinction reveals something important about the structure of reality: it has both depth and extension. The world is not merely a four-dimensional manifold of events spread across spacetime. It also has a vertical ordering at each moment—or at each region—where certain facts hold because of other facts in a non-causal, non-temporal sense. Recognizing this dual structure is essential for any adequate metaphysical theory.

Takeaway

Reality has two explanatory dimensions: a horizontal axis where causes produce effects across time, and a vertical axis where more fundamental facts constitute less fundamental ones at a time. Confusing the two obscures the genuine structure of the world.

Every explanation is backed by a relation that does the metaphysical heavy lifting. For causal explanation, that relation is causation. For metaphysical explanation, it is grounding. Understanding how these backing relations differ in their formal features is essential to keeping the two explanatory kinds apart.

Causation, as typically understood, relates events or occurrences. It is widely held to be contingent—the very causal chain that actually produced an effect might not have obtained. It is also defeasible: causal links can be disrupted by intervening factors. And causation is characteristically productive—causes bring about, generate, or produce their effects. Grounding, by contrast, relates facts. It is often taken to be necessitating: if the grounding facts obtain, the grounded fact must obtain. It is non-contingent in a way causation typically is not. And grounding is constitutive rather than productive—the grounding facts don't generate the grounded fact through some process; they make it the case that the grounded fact obtains.

The formal properties diverge further. Grounding is irreflexive (no fact grounds itself), asymmetric (if A grounds B, B does not ground A), and transitive (if A grounds B and B grounds C, A grounds C)—forming a strict partial order. Causation's formal profile is more contested. Some allow reflexive or symmetric causal relations in special cases, and the transitivity of causation is notoriously debated. These structural differences are not incidental; they reflect deep differences in the kind of dependence each relation captures.

What follows is that the explanatory force of causal and metaphysical explanations derives from fundamentally different sources. A causal explanation works by locating the event in a productive history. A metaphysical explanation works by revealing the constitutive structure that makes something the case. Conflating the backing relations leads to systematic confusion—attributing temporal dynamics to what is really a hierarchical ordering, or treating constitutive determination as though it were a species of efficient causation.

Takeaway

Grounding is to metaphysical explanation what causation is to causal explanation—but the two backing relations differ in relata, modal strength, and formal structure. Recognizing these differences prevents us from forcing one explanatory kind into the mold of the other.

Given that both causal and metaphysical explanation answer why-questions and both invoke relations of dependence, a natural proposal emerges: perhaps they are species of a single genus. Several philosophers have pursued this unification strategy. The idea is that there exists a general notion of explanation-backing determination, of which causation and grounding are particular instances—differing in their relata and temporal profiles but sharing a common core structure.

The case for unification is not trivial. Both grounding and causation exhibit directionality—a sense that the explanans is prior to the explanandum. Both support counterfactual reasoning: just as we say the window wouldn't have shattered if the rock hadn't struck it, we can say the singleton {Socrates} wouldn't have existed if Socrates hadn't existed. Both display a kind of non-monotonicity: adding further conditions can affect whether the explanation holds. These structural parallels suggest a shared explanatory architecture.

Yet the case against unification is formidable. The modal differences are significant: grounding is typically necessitating while causation is typically contingent. The relata differ: facts versus events. And the role of time is categorically different—essential for causation, irrelevant for grounding. If we try to capture both under a single genus, the resulting notion may be too thin to do any real work. We would have a formal schema that abstracts away precisely the features that make each relation explanatorily powerful.

The most balanced assessment may be that causal and metaphysical explanation share a family resemblance rather than a common essence. They are analogous without being homogeneous. Each tracks a genuine and irreducible form of dependence in reality. Attempts to reduce one to the other—or to subsume both under a single master concept—risk distorting the very phenomena they aim to illuminate. The philosophical landscape is better served by a pluralism about explanation that respects the distinct structures of the vertical and horizontal dimensions of reality.

Takeaway

Causal and metaphysical explanation share structural analogies—directionality, counterfactual sensitivity, non-monotonicity—but their deep differences in modality, relata, and temporality suggest they are genuinely distinct kinds of explanation rather than species of a single genus.

The distinction between metaphysical and causal explanation is not a pedantic exercise in classification. It reveals that reality has a richer structure than any purely causal picture can capture—a vertical dimension of constitution layered atop the horizontal dimension of temporal production.

Grounding and causation, as the backing relations for these two explanatory kinds, differ in their formal properties, their relata, and their modal profiles. These are not superficial differences but reflections of genuinely distinct forms of dependence woven into the fabric of the world.

A mature metaphysics requires both notions. To understand why the world is as it is, we must track not only what produced what, but also what constitutes what—how the fundamental gives rise to the derivative, right here, right now, without any lapse of time.