Causality

Causality describes how one thing—an event, process, state, or subject—helps bring about another, where the first is at least partly responsible for the second, and the second depends at least partly on the first. A cause can also be thought of as the reason behind what happens. Most processes have multiple causes, all lying in their past, and any effect can itself become a cause for future effects. This link between cause and effect often defines or is defined by the distinction between past and future; while physics tends to treat causality as following from time, some thinkers argue causality is more fundamental than time and space. The concept is an abstraction of how the world unfolds, basic enough that it often explains other progressions rather than being explained by them. It shares qualities with ideas like agency and efficacy, and grasping it may require an intuitive leap. Causality is built into everyday language and also appears explicitly in scientific notation.

In Aristotelian philosophy, "cause" translates the Greek *aitia*, meaning "explanation" or "answer to a 'why' question." Aristotle identified four types: material, formal, efficient, and final. Here, "cause" is the *explanans* for the *explanandum*, and confusing these types can lead to pointless arguments. Of the four, the efficient cause is closest to the modern sense of causality. David Hume, opposing rationalism, argued that pure reason cannot prove efficient causality; instead, he relied on custom and mental habit, claiming all knowledge comes from experience. Causality remains a central topic in philosophy today.

**Concept**

**Metaphysics** The nature of cause and effect falls under metaphysics. Immanuel Kant believed time and space preceded human understanding of the world's progression, and he also prioritized causality. However, he lacked the later insights from Minkowski geometry and special relativity, which show that causality can serve as a foundation for constructing time and space.

**Ontology** A key metaphysical question is: what kind of entity can be a cause, and what kind can be an effect? One view holds that cause and effect are the same kind of entity, with causality being an asymmetric relation between them—grammatically, you could say either "A causes B" or "B causes A," but only one is true. In process philosophy, every cause and effect is a process, event, or happening (e.g., tripping causes a broken ankle). Another view sees causes and effects as "states of affairs," with looser definitions. A more classical view, found in Aristotle, allows cause and effect to be different kinds: an action can cause an enduring object (e.g., parents' actions cause Socrates, a substance).

**Epistemology** Because causality is subtle, establishing it in specific cases requires evidence and intellectual effort. Hume argued the mind cannot directly perceive causal relations. He distinguished between the regularity view (X causes Y if they are constantly conjoined and X precedes Y) and the counterfactual view (X causes Y if, without X, Y would not exist). Hume saw the counterfactual view as ontological but advised using the regularity view as an epistemic definition to separate causal from noncausal relations. Contemporary philosophy divides causality into five main approaches: regularity, probabilistic, counterfactual, mechanistic, and manipulationist. All are reductive, defining causality in terms of other relations—empirical regularities, changes in probabilities, counterfactual conditions, underlying mechanisms, or invariance under intervention.

**Geometrical significance** Causality has the properties of antecedence and contiguity, which are topological.