The struggle between more theoretical approach to scientific explanation in medieval Oxford and the empirical and causal approach of Aristotle promoted in Paris, prepared the ground for the big change which came with modernity. The advance of the new science brought a gradual dominance of reductionist empiricism and rejection of causal explanation in metaphysics. The third part of the first segment of my special comprehensive exam depicts the way in which this change happened, in reference to five philosophers from that period.
René Descartes (1596-1650)
In order to understand methodology, ontology, and reflection on causality presented by Descartes, the father of the philosophy of classical science, we must remember that he was deeply rooted in Aristotelianism and scholasticism (deeper than it is usually acknowledged). He was particularly impressed with Aristotle’s demonstrative ideal of knowledge best exemplified in mathematics. His ambition was to apply this methodology to the physical sciences: “In physics I should consider that I knew nothing if I were able to explain only how things might be, without demonstrating that they could not be otherwise. For having reduced physics to mathematics, this is something possible …” (Oeuvres de Descartes). In order to make it happen he introduces a dualist ontology in which material substance is subject to mathematical, mechanical and deterministic description, and is distinguished from mind, which is unextended but capable of thought.
However, because he was rooted in Aristotle, Descartes saw scientific knowledge being not only demonstrative, but also explanatory, and therefore referred to causal description (even if he understood explanation only mechanistically). Thus, he would put an emphasis on experimentation and value hypotheses, saying in his Discourse that he finds experiments “more necessary in proportion as our knowledge advances.” He was indeed both a keen observer on nature and careful experimenter. He saw hypothesis as: a) being equivalent with mechanical explanation, or b) offering possible explanations of phenomena, or c) suggesting the “true cause” of phenomena based on experimental evidence. But this aspect of Descartes’ method would never hinder nor question his rationalism. In the end he would regard experiments as merely confirmatory and not capable of refuting conclusions that he arrived at by rational insight. He says that: “while our experiences of things are often fallacious, deduction (…) can never be wrongly performed by an understanding that is in the least degree rational” (Rules for the Guidance of our Native Powers). To sum up, we can say that we find in Descartes a philosopher trying to relate his a priori deductions to the actual world which he experienced and in which he performed his experiments. He would find the latter, practical part of his methodology, providing data for analysis and an opportunity for mind to gain an intuition of clear and distinct ideas underlying the particulars it has experienced.
Concerning philosophy of causation, while Aristotelian ideal of strict demonstration through causes permeates his work, Descartes rejects Philosopher’s fourfold notion of causality. Replacing the complex scholastic system of substantial forms, qualities of various kinds, elements, and other particles, with the clear and distinct idea that bodies are composed of particles in motion, he banishes formal and final causality (the latter he saw as being beyond human understanding). Though he still subscribes to material causality, he reduces it to basic physical constituents (rejecting “primary matter”), and eventually finds himself left with just one – efficient cause. Because it bears the burden of all other types of causation, Descartes develops a more complex theory of efficient causality. He distinguishes between the efficient cause of being and existence of all created things, which he attributes to God (efficiens and totalic causa), and efficient causes of various phenomena of the physical world (they have more explanatory power from the scientific point of view). His view of causation becomes deterministic. He sees the determinism of natural laws built into the efficacy of mechanical motion. Ends are predetermined by God and are opaque to human understanding, but through the laws that God predetermined “as the efficient cause of all things,” we can explain “the effects that we perceive by senses” (Principles of Philosophy).
Gottfried Wilhelm Leibniz (1646-1716)
Descartes won a great popularity among philosophers of his time. His method, including his causal reductionism, was followed by Hobbes, Gassendi, and Spinoza. However, there is one philosopher who would depart from this Cartesian tradition. Although Leibniz had followed in his early reflection the crowd of philosophers who valued mainly mechanical principles, he eventually changed his mind and become a defender of the plural notion of causality (which he defined in a manner that was peculiarly his own).
Leibniz’s early fascination with mechanical philosophy finds its best expression in the paper written in 1677 (On a Method of Arriving at a True Analysis of Bodies and the Causes of Natural Things), in which he states that: “since we may perceive nothing accurately except magnitude, figure, motion, and perception itself, it follows that everything is to be explained through these four.” Here we can see Leibniz who was convinced that through experimentation and observation one can arrive at the mechanical explanation which supplies ultimate “true causes” of phenomena.
About eighteen years later, in Specimen Dynamicum, Leibniz is less optimistic about mechanical character of scientific explanation. Reflecting on the causes of motion, he proposes a new solution through the idea of force. What is crucial here is that he treats force as something prior to extension, present everywhere and implanted by the Author of nature. He distinguishes between active and passive aspects of force, and thus goes back to formal and material causality as defined by scholastics. Active force is of two kinds: a) a primitive active force which is nothing more but the “first entelechy,” and corresponds to the soul or substantial form; and b) a derivative active force which is exercised through limitation of primitive force resulting from conflicts between bodies. Passive force is divided into two kinds as well: a) a primitive passive force which constitutes the very thing and resembles scholastic idea of materia prima; and b) a derivative passive force which is found mainly in inertia and resistance of secondary matter.
Leibniz further develops his defense of plural notion of causality in his justification of metaphysics. He says that matter cannot stand by itself and that mechanism needs intelligence and spiritual substance, for it did not come from a material principle and mathematical reasons alone. Here he introduces a reflection on final causality. There is no doubt that for him God is the ultimate cause of everything in the universe. But he does not follow the occasionalism of Malebranche and acknowledges that God put into things certain properties which explain all their predicates. God’s eternal law is carried out by the activity of creatures.
These developments of Leibniz’s metaphysics find another expression in his Monadology. The internal forces of monads can be identified with substantial form. When conceived as appetites, they have also a teleological character. The efficient causality of monads is not reciprocal. They cannot influence one another. That is why Leibniz introduces a rather vague idea of the principle of sufficient reason, which is supposed to explain the existence and relations between things (monads) apart from efficient causation (the meaning of both “sufficient” and “reason” is metaphysically unclear). The final cause of the order of monads and their characteristics is God. Although, according to his reflection in Monadology, efficient and final causality are complementary, Leibniz does not escape entirely the problem of determinism, which in his philosophy takes the form of a pre-established harmony.
David Hume (1711-1776)
Despite of Leibniz’s defense of formal and final causality, Descartes’ causal reductionism became more and more pervasive. It was followed by Locke, Newton, Berkeley, and Hume who is regarded by many as the one who gave the final blow to the theory of causation. While Berkeley argued against causal explanations (with reference to any kind of causation) in physical science, Hume generalized his opinion and applied it to natural philosophy and metaphysics, and thus did away with causality altogether. He claimed that given the concept of causal necessity, there is no way of justifying it rationally (causal necessity is not a logical necessity). He questioned three basic assumptions which he believed we accept in our notion of causation: 1) contiguity in space and time between cause and effect, 2) temporal priority of a cause to its effect, and 3) a necessary connection between cause and effect.
In his Treatise of Human Nature Hume assumes that every idea in our mind is based on a prior impression. That is why in order to justify our idea of causation, we must find the impression that gave rise to it. The idea of necessity has its source in many instances of similar occurrences. It is an outcome of constant conjunction which produces an association of ideas in our mind. Hume emphasizes that the tie of necessary connection “lies in ourselves, and is nothing but the determination of the mind, which is acquired by custom,” and which we tend to project onto the world. Here he gives two important definitions of cause: 1) a cause is “an object precedent and contiguous to another, and where all the objects resembling the former are placed in like relations of precedency and contiguity to those objects, that resemble the latter;” 2) a cause is “an object precedent and contiguous to another, and so united with it, that the idea of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other” (A Treatise of Human Nature). Because causal relations are not logically necessary, they cannot be known a priori. In order to determine whether there is a causal relation between A and B we must rely on our experience of similar relations. Thus, constant conjunction or regularity is both necessary and sufficient requirement for causation. Especially if we assume that “we never can, by our utmost scrutiny, discover anything but one event following another” (An Enquiry Concerning Human Understanding).
But Hume’s metaphysical and methodological position, as well as his opinion about causation, are not as clear and transparent as it is usually assumed. First of all, his embrace of the radical empiricism is accompanied by some rational implications. While he states that the mind is concerned only with its own ideas and cannot perceive anything of the reality outside itself (radical empiricism), he adds at one point that all our distinct perceptions are distinct entities (strong realism). Considering Hume’s theory of causation, Don Garrett (“Hume” in The Oxford Handbook of Causation) points towards three possible interpretations of his position: 1) causal projectivism – a projection onto cause-and-effect pairs of an element of felt necessity that does not resemble anything in these pairs, and is derived from the experience of constant conjunction (causation is mind-dependent); 2) causal reductionism – causality is reducible to constant conjunction, but constant conjunction is not alone sufficient for knowledge of causal relations and we have to know, a posteriori, that constant conjunction is what the causal sense detects; 3) causal realism – it is possible to argue that Hume can accept causal cognitivism while rejecting the semantic reductionism that treats causal claims as synonymous with claims about constant conjunction. Garrett claims that Hume “concedes something to the motivations of each of these packages, and he could with some justice be classified as subscribing to any of them, or all of them, or none of them – depending on the details of the more specific definitions that might be proposed for them.”
Immanuel Kant (1724-1804)
Kant found himself confronted with the rationalism of Leibniz and the empiricism of Hume, which he regarded as being in accord with Newtonian physics and philosophy, but incorporating to much of skepticism. Therefore, he was looking for a middle way which would implement both a priori elements of human knowledge stressed by rationalists, and the necessity of synthetic judgments based on the experience, emphasized in empirical circles. He sought a synthesis of these two approaches in a new type of judgment which is both synthetic and a priori. The price of this operation was significant. Since we can know a priori of things only what we ourselves put into them, synthetic a priori knowing “has to do only with appearances, and must leave the thing in itself as indeed real per se, but not known by us” (A Critique of Pure Reason).
Taking this position in his critical period Kant consequently and radically changes his way of philosophizing. While before Critique he was concerned with the problem as to how one substance acts on another, the problem of cause and effect, and the problem of space and extension as being constituted only by interaction of substances, in his present reflection substance as a basic explanatory principle is replaced by the a priori forms of sensibility and of understanding (he lists 12 of them). They are understood as the conditions of the possibility of experience, and are valid a priori for all objects of experience.
Following this methodological strategy Kant wanted to ground the principle of causality in the structure of reason. But in order to avoid the epistemologically disastrous consequences of the Humean criticism, he classified it as a principle explaining the synthetic a priori judgments of science. An event A is the cause of an event B iff there is a universal law which says that events of type A are necessarily followed by events of type B. But because neither the necessity nor the universality of the causal relation can be established empirically, it has to be grounded in the a priori conditions of judgment of a possible experience. Thus we can see that Kant rejects Hume’s view that we first perceive temporal succession between events, and only afterwards we are able to name one of them as cause, and the other as effect. For him the opposite is true. In order to establish an objective order of events in time, we need a priori synthetic concept of cause-effect relationships.
Summing up, we can say that Kant thought he have proved that concepts such as “cause” (“substance,” etc.) “stand a priori before all experience and have their undoubted objective rightness, though admittedly only in respect of experience” (Prolegomena to Any Future Metaphysics). For him every occurrence has a cause which is a prior event. The effect follows from the cause necessarily, and in accordance with a rule which is absolutely universal. All this is known to us a priori, but not without reference to experience.
Auguste Comte (1798-1859)
Despite of Kant’s struggle to save causation in epistemology and scientific explanation, the positive method in science and philosophy followed the way proposed by Berkeley and Hume, disposing of the search for causes. Positivists, in place of causes, searched only for correlations between facts which can be expressed in general laws of phenomena. Auguste Comte, who is one of the main representatives of the positivist camp, formulates his famous law of three stages: 1) theological or fictious, in which mind seeks the essential nature of beings, 2) metaphysical or abstract, in which mind replaces supernatural agents with abstract forces, and 3) scientific or positive, in which mind gives over the vain search for absolute notions and studies laws of natural phenomena (The Course in Positivist Philosophy). Although he endorsed the use of hypotheses, Comte accepted them only provided they were open to empirical verification. He stressed prediction rather than explanation as science’s primary aim. At one point he speaks very bluntly, leaving no doubt as to what he thinks about causal explanation: “The basic characteristic of the positive philosophy is that it regards all phenomena as subjected to invariable natural laws. Our business is – seeing how vain and senseless is any search into what are called causes, whether first or final – to pursue an accurate discovery of these laws, with a view to reducing them to the smallest possible number” (The Course).
In spite of his radical rejection of causality, Comte did not reduce his “positive philosophy” merely to induction. He still valued deduction for establishing particular conclusions related to special topics of research, and as an essential tool of making predictions. For this reason, we can venture to say that Comte in fact followed the path of those post-Cartesian philosophers who hoped to steer a middle course between empiricism and rationalism. Nevertheless, it seems that nothing was really able to change the course that philosophy of science took after Descartes, which led to the decline and final dismissal of causal explanation in phenomenalism, conventionalism, operationalism, and the orthodox interpretation of quantum mechanics. However, the story does not end up with these trends in philosophy. Causality is coming back on stage with anti-Humean tendencies and the return of realism, accompanied by some contemporary reflections on causality within the analytic tradition. But this is a material for yet another story.