Science

Aristotle's account of science in the Posterior Analytics sets the standard for the entire Western tradition. Scientific knowledge (episteme) is distinguished from mere belief and from skill (techne) by its necessary character: to know something scientifically is to know that it is so and why it could not be otherwise. This requires demonstrative proof from first principles that are themselves necessarily true, primary, and prior.

The structure of an Aristotelian science is hierarchical. Each science has its own first principles (axioms and definitions appropriate to its subject matter) which cannot be derived from a more general science. Physics has its own principles; mathematics has different ones; biology has others. The principles are known by induction, but once known, all further truths in the science are derived by demonstration. Science thus proceeds from the universal and necessary to the particular.

The physical sciences add a further requirement: knowledge of causes. Aristotle identifies four types of cause (material, formal, efficient, final) and argues that genuine scientific explanation must exhibit the relevant cause. Physics without teleology is incomplete; to explain why wood burns, one must give its material constitution, its form as combustible matter, the flame applied to it, and the end-state produced. This teleological requirement will be the first target of the scientific revolution.

Aristotle's conception of science as demonstrative knowledge from necessary causes dominates the tradition until Bacon. The objections are partly logical (why must all scientific knowledge be demonstrative?) and partly empirical (the natural world turns out to be more contingent and probabilistic than Aristotle imagined).

Aquinas inherits Aristotle's account of science and deploys it in a surprising direction: to argue that theology is a science. This seems paradoxical: theology's first principles are articles of faith, not self-evident axioms. But Aquinas uses the Aristotelian concept of a "subalternate science" to defuse the paradox. Just as music is subalternate to arithmetic (it borrows its principles from a higher science), so theology is subalternate to the science of God and the blessed, who know divine truths by direct vision.

This move preserves the Aristotelian structure while making room for revelation. Sacred doctrine does not need to demonstrate its first principles; it receives them from a higher authority. Once accepted, it can proceed in the manner of any other science: drawing inferences, resolving objections, organizing knowledge systematically. The Summa Theologica is the systematic product of this method, an attempt to derive a systematic account of Christian teaching from its revealed premises.

Aquinas also distinguishes theology from natural philosophy and mathematics. Natural philosophy deals with changeable, material things; mathematics with abstracted quantities; theology with things that altogether transcend sense. The methods appropriate to each differ accordingly. Empirical observation is suited to natural philosophy; it is not the primary method for theology. This division of the sciences by subject matter will be challenged when Bacon insists that all natural knowledge must be empirical.

Aquinas's integration of Aristotelian science with Christian theology shapes the medieval university and remains the target of early modern reform. Bacon's attack on Aristotle is also, implicitly, an attack on the Scholastic synthesis that Aquinas represents.

Bacon's program for the reform of the sciences is at once epistemological and practical. Epistemologically, he argues that the Aristotelian sciences have failed because they rest on general notions hastily abstracted from experience and confirmed by disputation rather than by renewed contact with nature. Practically, he argues that the purpose of knowledge is not contemplation but "the relief of man's estate," the improvement of human life through mastery of natural processes.

His diagnosis of failure is organized around the "idols," systematic distortions that afflict the human understanding. Idols of the Tribe (tendencies shared by all humans, like the preference for order and constancy), Idols of the Cave (individual biases), Idols of the Market Place (confusions arising from language), and Idols of the Theatre (deceptive philosophical systems). Each idol causes a different kind of distortion in natural inquiry.

The remedy is twofold. Negatively, the idols must be identified and expelled. Positively, a new method of patient, systematic induction from carefully collected observations must replace both deductive system-building and anecdotal experience. Bacon's vision of collaborative science (institutionally organized, publicly funded, operating through systematic natural histories) anticipates the organization of modern research. Science as a collective, cumulative enterprise rather than individual speculation is Bacon's most lasting contribution.

Bacon's deepest tension is that he dismantles one authority — Aristotle — and proposes to replace it with method, trusting that disciplined observation will converge on truth. Descartes, reading Bacon, will agree that the old learning must go but conclude that observation alone is too weak a foundation; genuine science must start from indubitable first principles reached by pure reason, not from the patient accumulation of natural histories.

Descartes shares Bacon's dissatisfaction with Aristotelian science but draws a different conclusion. The problem is not that the method is too deductive and too little empirical, but that it is not deductive enough: it uses deduction without first securing the foundations from which deduction must proceed. Genuine science, on the model of mathematics, begins from indubitable first principles and proceeds by clear and necessary reasoning.

His method of systematic doubt is designed to find those first principles. Strip away everything that can be doubted; what remains (the cogito) is indubitable. From the cogito he proves the existence of God; from God he derives the reliability of clear and distinct perception; from that he derives the laws of motion and the mechanical philosophy of nature. Science is a tree: metaphysics is the roots, physics the trunk, the specific sciences the branches.

This unified science differs from Aristotle's in a crucial respect: it applies a single method to all subjects. Aristotle's sciences were divided by subject matter, each with its own first principles. Descartes' mathesis universalis applies the method of clear reasoning to everything. This drives the mechanistic program: all natural phenomena, including biology, are to be explained by the same laws of matter in motion that govern physical bodies.

Descartes' mechanical philosophy becomes the dominant paradigm of seventeenth-century science. But the demand for a priori certainty clashes with the actual practice of natural philosophy. Newton will achieve the greatest scientific synthesis of the period by working empirically, not by deducing from indubitable first principles.

Newton's Principia is the paradigm of scientific achievement that all subsequent philosophy of science must account for. Its combination of mathematical precision, empirical grounding, and extraordinary explanatory power made it the standard against which all claims to scientific knowledge were measured for two centuries.

Newton's philosophical statements are characteristically modest and empiricist. His four Rules of Reasoning counsel parsimony in positing causes, uniformity in assigning causes to effects, and restraint in generalizing beyond the phenomena. His rejection of hypotheses is not a rejection of mathematical reasoning but of metaphysical speculation about hidden mechanisms beyond what observation can warrant. Gravity is a real force acting according to an inverse-square law: the phenomena establish this. Whether it is material, immaterial, or a manifestation of God's will, Newton refuses to say.

This creates the peculiar character of Newtonian science: mathematically rigorous and empirically grounded, yet deliberately agnostic about the underlying metaphysics. The laws are mathematical relations among observable quantities; their physical interpretation is left open. This combination was enormously productive but philosophically puzzling: what licenses the inference from observed regularities to universal laws? Hume will ask this question directly.

Newton gives science its modern shape: experimental, mathematical, and publicly verifiable. The philosophical questions he leaves open become the central problems of eighteenth-century philosophy, from Hume's problem of induction to Kant's transcendental deduction of the categories.

Hume's epistemology produces a stringent criterion for scientific knowledge. All human knowledge divides into two kinds: relations of ideas (mathematics and logic, demonstratively certain) and matters of fact (empirical sciences, established by experience and always subject to revision). No third kind is possible. Claims that are neither demonstrably certain nor empirically testable (traditional metaphysics, dogmatic theology) are not genuine knowledge.

His famous closing passage of the Enquiry makes the challenge explicit. Take any volume of divinity or school metaphysics. Does it contain abstract reasoning concerning quantity or number? Does it contain experimental reasoning concerning matter of fact and existence? If not, commit it to the flames, for it can contain nothing but sophistry and illusion. This empiricist principle condemns most of traditional philosophy, including much of what Aquinas and Descartes put forward as knowledge.

Hume is not purely destructive. He proposes a positive science of human nature, a moral philosophy modeled on Newton's natural philosophy, proceeding from careful observation of human behavior rather than from speculative first principles. Passions, beliefs, and social practices are natural phenomena that can be studied empirically. The science of man is the foundation of all the other sciences, since all knowledge depends on the human faculties that produce it.

The challenge Hume leaves unanswered is one he himself identified: if all knowledge of matters of fact rests on induction, and if induction cannot be rationally justified without circularity, then natural science itself cannot meet the very criterion he proposes for it. Kant, jolted from his dogmatic slumbers by precisely this problem, will try to show that causal reasoning is neither an empirical habit nor a groundless assumption but a condition built into the structure of experience itself.

Kant defines genuine science by the criterion of necessity and universality. Empirical generalizations are always contingent; they might have been otherwise. Mathematical truths are necessary but, according to Kant, they are also synthetic: they extend our knowledge beyond what is contained in the concepts alone. Scientific knowledge must be both: necessarily true and genuinely informative about reality. This is what Kant calls synthetic a priori cognition.

His answer to Hume's challenge is that the mind does not simply observe regularities but actively imposes its forms on experience. The categories of the pure understanding (including causality) are not derived from experience but are the conditions under which experience is possible. Nature must conform to these conditions because nature, for us, is experience organized by the understanding. The laws of nature are not read off from phenomena; they are prescribed to phenomena by the cognitive framework we bring to experience.

This is the "Copernican revolution" in philosophy: instead of knowledge conforming to objects, objects conform to the forms of our cognition. It secures the necessity of natural science at the cost of restricting knowledge to the world of possible experience. We can have science only of the phenomenal world, things as they appear under the forms of sensibility and the categories. The thing in itself remains unknowable.

Kant's philosophy of science generates two divergent traditions: the idealist line (Hegel, who will dynamicize Kant's static categories) and the empiricist line (Mill, who will reject the a priori altogether). Both must wrestle with the question of how science relates to reality as it is in itself.

Mill's philosophy of science is the definitive statement of empiricism in the nineteenth century. Against Kant, he denies that any knowledge is a priori: even the laws of logic and mathematics are inductive generalizations, though confirmed by more instances than any other kind. Against the rationalist tradition, he insists that the methods of science are continuous with ordinary practical reasoning from experience, not fundamentally different in kind.

His System of Logic argues that science is distinguished from common sense not by a different faculty or source of knowledge but by a more disciplined application of the same methods. The five canons of induction make explicit the logic implicit in successful practical reasoning. They are the rules of what good thinkers have always done, formalized and made available for criticism. The syllogism, which Aristotle placed at the center of science, Mill reinterprets as an inference from particular to particular mediated by a general record of observed cases.

Mill extends inductive logic to the social and moral sciences in Book VI, arguing that the logic appropriate to the study of human society is not fundamentally different from that of natural science, though the complexity of social phenomena makes it practically harder to apply the canons. He calls for a "science of character" (ethology) that would establish the laws of the formation of human character and make possible a genuine science of society.

Mill's ambition to extend inductive canons to the science of human character reveals a tension he cannot resolve: the same individual whose freedom On Liberty insists on resisting external determination is, in the System of Logic, the product of laws of character formation that make him predictable in principle. Freud will inherit this tension and try to turn it into a clinical method, treating the unconscious as a natural system subject to scientific investigation while still speaking of the patient's freedom to change.

Freud concludes the tradition's debate about science with a declaration of positivism as uncompromising as any in the philosophical record. In his New Introductory Lectures, the final lecture turns to the question of a Weltanschauung, a comprehensive view of life and the world. The scientific Weltanschauung is the only coherent one: "there is no other source of knowledge of the universe but the intellectual manipulation of carefully verified observations."

His targets are religion and philosophy. Religion makes claims about reality that cannot be verified by observation; it substitutes authority for evidence and wish-fulfillment for demonstration. Philosophy, though it sometimes behaves as if it were a science, typically aspires to something science must deny itself: a complete and coherent picture of the universe arrived at without exhaustive investigation. Both fail the test of the scientific Weltanschauung: the willingness to proceed only as far as evidence warrants, to revise conclusions when evidence demands, and to hold hypotheses provisional.

Freud's positivism is not merely methodological but historical: science is the most successful response humanity has ever found to the fundamental desire to understand. It cannot satisfy the emotional needs that religion addresses, and it makes no promise of comfort. But it is the only path to genuine knowledge. The passage from religious to scientific Weltanschauung is the defining intellectual movement of modernity, and there is no going back.

Freud's declaration marks the endpoint of the tradition's internal debate about science and sets the terms for the twentieth century. Logical positivism will systematize his empiricist criterion; the philosophy of science from Popper onward will complicate and in many ways overturn both.