Causal Order and Temporal Order

Core Idea

Do causal relations presuppose temporal order, or is temporal order derivative of causal structure? Standard metaphysics assumes causes precede effects temporally, but some theories reverse this. Others argue causation and temporal direction are asymmetric for distinct reasons (causation involves counterfactual dependence, time has entropic direction). Understanding this relationship is crucial for philosophy of time and causation.

Explainer

The commonsense picture is straightforward: causes come before effects, and "before" is defined by the direction of time. But once you've studied causation and the philosophy of time separately, a deeper puzzle emerges: how exactly do these two asymmetries — causal and temporal — relate to each other? Are they the same asymmetry, or are they independent features of the world that merely happen to align?

One position is that causal order is prior to temporal order — that what we call "earlier" and "later" is actually constituted by the direction of causal influence. On this view, to say event A is earlier than event B just is to say something like "A can causally affect B but not vice versa." This is the causal theory of time, associated with philosophers like Reichenbach. It has a certain economy: it reduces temporal direction to causal direction, avoiding a primitive "arrow of time." But it faces a serious challenge: it threatens circularity. Our analyses of causation — including the counterfactual analysis you've already studied — typically presuppose temporal direction. If causes are defined in terms of counterfactual dependence and counterfactuals already assume "earlier" and "later," then we can't also define temporal order in terms of causes without going in a circle.

The alternative is to treat the temporal asymmetry as prior or as grounded in something independent — most commonly, thermodynamics. The second law of thermodynamics says entropy increases in the forward time direction. Low-entropy states are vastly outnumbered by high-entropy states, so systems naturally evolve toward disorder. This entropic arrow of time can explain why causes precede effects statistically without needing causal order to ground temporal order. On this picture, time's direction and causation's direction are both grounded in the same underlying fact about entropy and probability, but they are not identical.

A third wrinkle involves backward causation — the possibility that effects could precede their causes. Standard physics is time-symmetric at the fundamental level; the laws of mechanics work equally well in both temporal directions. Some interpretations of quantum mechanics and certain theoretical proposals in physics allow for retrocausal influence. If backward causation is genuinely possible, this suggests that causal order and temporal order are conceptually separable: we can coherently imagine a cause that comes after its effect, which means neither concept fully reduces to the other. The relationship between causal and temporal asymmetry thus sits at the intersection of metaphysics, physics, and the analysis of counterfactuals — a point where the questions you've studied in each domain converge on a single deep puzzle about the structure of reality.