Cause

Plato's treatment of causation proceeds from a distinction between the true causes or reasons of things and the material conditions that accompany them. In the Phaedo, Socrates recounts his early disappointment with the natural philosophers: they explained that he sat in prison because of the configuration of his bones and sinews, but this, he says, is not the true reason. The genuine cause of his remaining in prison is that it is best for him to do so. The bones and sinews are conditions without which the cause could not operate, but they are not the cause itself.

Plato identifies true causes with Forms and the Good. To explain why a thing is what it is, one must point to what it participates in, that is, to its intelligible nature, and ultimately to the Good, which is the source of intelligibility itself. The Timaeus applies this account to the cosmos: the world is fashioned by the Demiurge, who works upon pre-existing matter by taking eternal Forms as his model, because he is good and desires that all things should be as good as possible.

This gives causation a teleological and formal orientation from the outset. The question why is, on this view, prior to the question how, and the answer lies in form and purpose rather than in matter and motion alone. Material conditions are real and may be investigated, but they are subordinate to the principal explanation. The distinction between genuine or principal causes and material or auxiliary conditions is one that Aristotle will develop into his doctrine of the four causes.

Plato's account of causation is developed by Aristotle, who systematizes the types of cause and extends the inquiry to natural things generally. Aquinas draws on both when considering causation in relation to creation, particularly on the question of whether the Good can be identified with God as First Cause.

Aristotle holds that to know something fully is to know it through its causes, and he distinguishes four. The material cause is what a thing is made of, as bronze is the material cause of a bronze statue. The formal cause is what it is to be that thing, its shape or essence. The efficient cause is what brings it into being, as the sculptor produces the statue. The final cause is that for the sake of which the thing exists or comes to be, the end toward which it is directed.

Aristotle applies this framework to natural things as well as to artifacts. In nature, he argues against the atomists, things are not produced by chance arrangements of matter; natural things have ends internal to themselves. An acorn grows into an oak not by accident but because its form is directed toward its proper end. Teleology, on this account, is not imposed on nature from outside but belongs to the nature of living things. To understand any natural change fully, one must identify all four causes operative in it.

The four causes provide the framework within which Aristotle's inquiries into nature, soul, and being proceed. In the Physics, efficient and final causation receive the most detailed treatment in the context of natural motion and change. In the Metaphysics, formal causation is reconsidered in connection with substance and essence. The question of whether efficient causation in nature requires a first unmoved mover connects the doctrine of the four causes to Aristotle's natural theology, as discussed further under the idea of God.

Aristotle's fourfold analysis of causation remained the standard framework in natural philosophy and theology through the medieval period. In the seventeenth century, formal and final causes were set aside by natural philosophers in favor of an account of nature in terms of matter and efficient causation alone. The question of whether this reduction is adequate to explain living and conscious things recurs throughout modern philosophy.

Augustine's treatment of causation is shaped by the doctrine of creation from nothing, which introduces a kind of causality not found in Aristotle's analysis. For Aristotle the world is eternal; the question of a cause of the world's very existence does not arise. For Augustine, the world was created by God from nothing, and divine causality differs in kind from every form of natural or human causation. When a craftsman makes a table, he works on pre-existing matter; when God creates, there is no prior matter to work on. The efficient cause in this case gives not form to matter but being to what would otherwise simply not exist.

This claim has consequences for the analysis of natural causes. Augustine distinguishes the initial act by which God calls the world into existence from the subsequent processes of natural change. Natural causes, the motion of the sun, the growth of seeds, the generation of animals, are real causes, but they operate within an order that is itself continually sustained by divine causality. The world does not run of its own momentum once created; it requires God's concurrent action at every moment to persist in being. Conservation is, on this account, a kind of continued creation, and every secondary cause is dependent not merely for its initial impulse but for its ongoing efficacy.

Augustine also introduces the notion of rationes seminales, seminal principles embedded in matter at creation, by which later forms emerge in their proper time. These are causal powers latent in matter, placed there by God, awaiting the conditions for their actualization. Through them, natural development can unfold without requiring a continuous miraculous intervention, while still remaining a consequence of the original creative act. The relation between these latent principles and the development of natural forms is taken up by later medieval thought in connection with the question of how divine causation and natural causation cooperate.

Aquinas will take up Augustine's account of creation as unique causality and of conservation as continued creation, developing both the distinction between essentially and accidentally ordered causal series and the doctrine of how God's causality relates to that of creatures without displacing it. The question of how a first cause that gives being itself can also leave room for genuine creaturely agency is one that theology and philosophy have returned to repeatedly in the tradition following Augustine.

Aquinas applies Aristotle's doctrine of the four causes to the theological question of God's relation to the world. The Five Ways in the Summa Theologica are arguments from causation: from motion, from efficient causality, from contingency, from gradation, and from final causality. In each argument, he holds that a series of dependent causes cannot regress infinitely; there must be a first member, on whom all others depend, whom we call God.

Aquinas also distinguishes essentially ordered from accidentally ordered causal series. In an accidentally ordered series, such as father begetting son who begets grandson, each cause, once it has acted, need not continue to act for the subsequent effects to follow. In an essentially ordered series, such as a hand moving a stick that moves a stone, every cause in the series must be actively operating at the same moment, or the effect ceases. The universe, on Aquinas's account, is an essentially ordered series in which God is active at every moment, not merely as a prior cause but as the concurrent cause of all creaturely causation.

Creation, therefore, is not a past event that God brought about and then left to operate on its own, but a continuous conservation: God is the First Cause not merely in the order of time but in the order of being, the source that gives existence to every cause as it acts. The causality of secondary causes is real but entirely dependent, so that the same effect may be attributed both to God and to the creature, each in its own mode.

Aquinas's account attempts to hold together the full reality of secondary causation with the absolute priority of the First Cause. The question of how divine and creaturely causation are related without either absorbing the other is one that subsequent theology has continued to discuss, and is treated further under the ideas of God and Necessity and Contingency.

Bacon argues that the habit of explaining natural phenomena by appeal to purposes has arrested the growth of knowledge by giving investigators the appearance of explanation where none has been achieved. In The Advancement of Learning he charges Plato, Aristotle, and Galen with "intercepting the severe and diligent inquiry of all real and physical causes" by introducing final causes into physics. Final causes are not false, he concedes; they are appropriate to ethics and theology but misplaced in the investigation of nature, where they tend to foreclose inquiry rather than advance it.

Bacon's proposed reform divides natural philosophy according to the kinds of cause appropriate to each part. Physics is concerned with material and efficient causes, the proximate and particular agencies that produce effects; what Bacon calls "metaphysics" in his revised sense is concerned with formal and final causes. But his sense of "form" differs significantly from Aristotle's: a Baconian form is not the essence of a substance but the invariable law governing a nature or property, the rule that constitutes heat or whiteness or gravity in all its instances. To discover the form of a nature is to discover the law under which it operates universally. This reorientation of formal inquiry toward laws of nature, rather than essences of things, aligns with the mathematical-physical conception of natural law that develops from Newton onward.

Bacon endorses the mechanical philosophy of Democritus, praised for attending to the "particularities of physical causes" rather than intermingling final causes with physics. His own method, however, differs from the geometrical deductive approach of Descartes and Newton: the Novum Organum sets out a method of induction by tabulation and systematic exclusion of instances, aimed at discovering forms and natures underlying observed phenomena through careful comparison of cases.

Bacon's restriction of natural philosophy to efficient and formal (in his revised sense) causes influenced the assumption, common in the subsequent tradition, that natural science is properly confined to these two types of explanation. Descartes inherits the restriction on final causes in physics, though he grounds it differently; Newton inherits the empirical orientation and the focus on laws derivable from phenomena. Whether the exclusion of final causation from natural science requires or entails its exclusion from the account of living organisms and human action is a question that recurs from Kant's Critique of Teleological Judgment to contemporary philosophy of biology.

Descartes draws on a principle he regards as self-evident: there must be at least as much reality in the efficient and total cause as in the effect. Nothing comes from nothing, and more cannot come from less. In the Third Meditation, he applies this principle to his own idea of God, an idea of an infinite and perfect being. Such an idea has more objective reality than any finite thinker could produce from his own resources; only a being with at least as much formal reality as the idea represents could have placed it in him. God therefore exists as the cause of the idea of God.

In his account of the natural world, however, Descartes narrows the range of causes admitted by natural science. Formal and final causes, central to Aristotle's physics, are set aside. Nature is to be explained in terms of matter in motion, governed by mechanical laws. Final causes belong, Descartes holds, to God's inscrutable purposes, which lie beyond human inquiry; he counsels that we "should abstain entirely from searching out the final causes of natural things." Only efficient causation remains an appropriate category for natural science.

This produces a sharp division between natural inquiry and theology. God is invoked to explain the origin and conservation of the mechanical order, but within that order final causes have no scientific role. Whether this account is adequate to explain biological processes and purposive behavior, and whether it can be consistently maintained alongside the theological use of causal principles, became central questions in the philosophy of nature following Descartes.

Descartes's restriction of physical inquiry to efficient causation, combined with his use of causal principles to argue for God's existence, presents a divided account: the theological argument depends on a rich notion of degrees of reality, while the physical account dispenses with the formal and final causes that gave causal explanation its full Aristotelian content. Spinoza will press the restriction further, arguing that even the divine will involves no purposes, and that causation throughout nature is identical with logical necessity.

Spinoza holds that from a given cause an effect follows necessarily, and that the order and connection of ideas is the same as the order and connection of things. To cause and to be a reason for are, on this account, the same relation. The world is a single necessary consequence of God's nature, understood geometrically, and every particular thing or event follows from God with the same necessity that theorems follow from definitions.

This identification of causation with logical necessity eliminates final causation entirely. Things do not happen for the sake of anything; they follow from the infinite necessity of substance. Human purposes are real as modes of thought, but they do not alter the physical order, which follows its own necessity. Nature acts neither for an end nor by choice; it simply is, and everything in it follows from what it is. God is a free cause because nothing outside him determines him, but he is not free to act otherwise than he does; freedom, for Spinoza, is self-determination rather than the ability to choose between alternatives.

Whether such a universe, in which every event follows with logical necessity from the divine nature, can accommodate genuine human agency or genuine contingency in the world is a question Spinoza's readers have persistently raised. The implications for human freedom and moral responsibility are discussed further under the ideas of Liberty and Necessity and Contingency.

Spinoza's identification of causation with necessary logical consequence distinguishes his account from Hume's, who holds that no observation of the world can reveal necessity in the relation between events. Where Spinoza derives causal necessity from the nature of substance a priori, Hume will argue that the idea of necessary connection is not given in any impression and cannot be found in the objects themselves.

Newton's most consequential statement on causation is a refusal: "I feign no hypotheses." At the conclusion of the Principia, he declines to speculate about the underlying cause of gravitational attraction. He has derived the law — every body attracts every other body with a force proportional to their masses and inversely proportional to the square of the distance — from the phenomena of planetary motion and terrestrial mechanics. What produces that attraction, whether it is material contact, an ethereal medium, or action at a distance, he does not claim to know, and he regards the search for hidden mechanical causes as belonging to a species of inquiry that natural science cannot reliably prosecute. To derive general principles of motion from phenomena is "a very great step in philosophy," even if the causes of those principles remain undiscovered.

This position represents a deliberate narrowing of what science undertakes relative to the Aristotelian and scholastic traditions. For Aristotle, genuine scientific knowledge requires knowledge of causes; the Posterior Analytics holds that a demonstration is scientific only if it proceeds through the relevant cause. Newton does not deny that causes exist, but he distinguishes the task of formulating mathematical laws that accurately describe phenomena from the metaphysical question of what generates those laws. The Rules of Reasoning at the opening of Book III of the Principia counsel assigning no more causes than are sufficient to explain phenomena and assigning the same causes to the same kinds of effects — principles of economy and uniformity that guide induction without committing to any particular causal ontology.

In practice, Newton does attribute phenomena to forces, including gravity, inertia, and the forces operative in optical and chemical experiments. These are mathematical entities defined by their measurable effects; whether they correspond to genuine physical powers or merely summarize observed regularities is a question Newton's methodology deliberately leaves open. The tension between his mathematical-physical practice and the metaphysical claims embedded in concepts like force and attraction was felt immediately by his contemporaries and continues to be discussed in the philosophy of science.

Newton's restriction of natural science to mathematically formulated laws derivable from phenomena, rather than causal explanations of the mechanisms behind them, feeds directly into Hume's analysis. Hume, who admired Newton's method and aspired to do for human nature what Newton had done for the physical world, radicalized the epistemic modesty: if even Newton's physics proceeds without knowledge of ultimate causes, then perhaps the concept of causation itself involves a claim — necessary connection — that observation never warrants.

Hume's examination of causation begins from his general principle that all ideas must be traced to antecedent impressions. He asks what impression gives rise to the idea of necessary connection between cause and effect. When we examine any case of what we ordinarily call causation, such as one billiard ball striking another, we find three observable features: contiguity in space and time, succession of the cause before the effect, and constant conjunction of such events in past observation. What we do not observe is any impression of necessary connection between the cause and the effect as such.

Since no impression of necessary connection is discoverable in the objects, Hume traces the idea to its actual source: the habit of the mind. When one kind of event has always been followed by another, the mind, upon perceiving the first, comes to expect the second. This felt expectation or determination of thought is then projected onto the objects and called a causal connection. Causation, on this account, is partly a feature of the observer's psychology: the necessity we attribute to causes is not in the objects but in the mind's propensity to pass from one to the other.

The consequences Hume draws from this analysis are considerable. The inference from cause to effect is not a rational demonstration but a custom; it cannot be justified by reason alone. The expectation that the future will resemble the past, which underlies all causal inference, cannot itself be rationally grounded without circularity. Induction and natural science depend, therefore, on habit rather than on demonstrative reasoning. These implications for the foundations of empirical knowledge are discussed further under the ideas of Induction and Knowledge.

Hume's analysis relocates the necessity of causation from the objects to the observer, making causation partly a feature of human psychology and habit rather than of the external world. Kant held that Hume had drawn the wrong conclusion from a correct observation, and that the necessity attributed to causation is real but is contributed by the mind as a condition of experience rather than derived from experience.

Kant holds that Hume's account of causation is correct in observing that we do not perceive necessary connection in the objects themselves, but draws the wrong conclusion from this. Hume, taking the absence of any impression of necessity as evidence that the idea of causation is a product of habit, was prepared to leave science resting on mere custom. Kant argues that this conclusion, while following from Hume's empiricist premises, fails to account for the character of scientific knowledge.

In the Second Analogy of the Critique of Pure Reason, Kant argues that without the category of causation, we could not distinguish an objective sequence of events from a merely subjective sequence of perceptions. For an event to count as something that has objectively occurred, something whose order is not reversible at will, it must be conceived as following from a prior state according to a rule. Causality is thus a condition under which experience of objective events is possible, not a generalization from such experience. The necessity of the causal relation is contributed by the understanding as a form of thought, not derived from observation.

This account preserves the universality and necessity of causal law within experience, while restricting its application to the field of appearances. Within possible experience, every event has a cause, necessarily. About things-in-themselves, the category of causation cannot be applied; and freedom, conceived as a causality not subject to the causal order of appearances, can at least be thought of without contradiction, even if it cannot be known theoretically. The compatibility of natural causation and freedom is discussed further under the ideas of Liberty and Will.

Kant's solution assigns causal necessity to the mind's contribution to experience rather than to the objects themselves, thus avoiding both Hume's sceptical conclusion and the rationalist claim that necessity can be derived a priori from the nature of things. Whether this resolution, which restricts causation to the field of possible experience, adequately accounts for the explanatory role causation plays in natural science, was a question that occupied Kant's successors.

In the Science of Logic, causation appears within the Doctrine of Essence as one of a series of relations, including substance and accident, cause and effect, and reciprocity, each of which is shown to be inadequate in isolation and to pass over into a more complete determination.

The inadequacy of the simple cause-and-effect relation lies in its mutual dependence: a cause is a cause only by producing its effect, and an effect is an effect only by proceeding from its cause; each requires the other for its own determination. This mutual conditioning constitutes what Hegel calls reciprocity. When reciprocity is developed further, it gives way to the category of organic development, in which moments do not act on one another from without but unfold an internal purpose.

It is at this level that Hegel's account re-admits teleological explanation, which Bacon and Descartes had sought to confine within ethics and theology and to exclude from the investigation of nature. Mechanical efficient causation holds at its own level but is, on Hegel's account, a limited form of explanation when applied to living, conscious, or historical reality. The deeper logic of reality is purposive: Spirit moves not by external compulsion but by an internal necessity directed toward self-knowledge.

Whether Hegel's reinstatement of teleological explanation at the level of Spirit is compatible with Kant's restriction of causal categories to the field of appearances is a question that Hegel's own account raises but does not resolve on Kantian terms. The relation between mechanical causation and the teleology of historical development is discussed further under the ideas of History and Necessity and Contingency.

Mill's account of causation in the System of Logic proceeds from the same empiricist foundations as Hume's but refines them in the direction of scientific practice. A cause, on Mill's analysis, is not a single antecedent event picked out by ordinary speech but the full assemblage of conditions, positive and negative, whose presence invariably and unconditionally produces the effect. Ordinary usage selects one condition from this assemblage, typically the one that varied most recently or most noticeably, and calls it the cause; but all conditions are equally parts of the cause in the logical sense.

From this analysis Mill derives his Methods of Experimental Inquiry: Agreement, Difference, Residues, and Concomitant Variations. These methods formalize the procedures by which causal connections are discovered from observed regularities. Agreement identifies the common antecedent among cases sharing an effect; Difference isolates the condition whose presence or absence marks the distinction between cases that exhibit and cases that do not exhibit the phenomenon. The Methods are, in effect, a systematic development of Hume's analysis of constant conjunction given sufficient rigor to guide scientific investigation.

Mill holds that causation requires no Aristotelian forms, Cartesian concurrence, or Kantian a priori categories. What science means by a causal law is an observed unconditional sequence, established by induction and extended to unobserved cases on the assumption that nature is uniform. Mill acknowledges that the uniformity of nature cannot itself be proved by induction without circularity; he treats this uniformity as the fundamental postulate of empirical inquiry rather than as a defect to be remedied by prior philosophy.

Mill's reformulation of Hume's analysis in terms of conditions and experimental methods brought the empiricist account of causation into closer alignment with the requirements of scientific practice. The problem of induction that his account leaves unresolved is discussed further under the idea of Induction. Whether the plurality of causes, which Mill acknowledges as a complication for experimental methods, is compatible with the universality required of scientific law is a question that recurs in later philosophy of science.