Overview
Reason in Common Sense is the opening volume of George Santayana’s The Life of Reason, or The Phases of Human Progress, the multi-volume work in which he sets out a naturalistic account of human culture. Where the later volumes treat reason as it appears in society, religion, art, and science, this first volume treats reason at its most elementary: in the ordinary, practical understanding of the world that Santayana calls common sense. The book’s project is to show how reason — usually imagined as a faculty opposed to instinct, or as a supernatural gift — actually grows out of animal impulse and becomes the organizing principle of a human life.
The volume’s controlling idea is that reason is not a separate power but a development of instinct. Experience begins as a “flux” — a stream of sensations, feelings, and impulses, each momentary and unrepeatable. Reason appears when the mind, aided by habit and memory, begins to abstract stable forms (“essences”) from this flux and to combine them into “concretions”: the objects, causes, and selves that make up a world. Common sense is the first fruit of this process — the working picture of a world of enduring things, causal connections, and a self among them, which human beings take for granted in everyday life.
The introduction sets out this general conception and contains the volume’s best-known sentence, that “those who cannot remember the past are condemned to repeat it.” The chapters that follow trace, step by step, the birth of reason out of the flux, the discovery of essences, the formation of the ideas of matter and nature, the emergence of the idea of the self, and the appearance of the ideal as the standard by which reason measures experience and directs conduct. Santayana presents these as “phases” of human progress rather than as timeless truths: common sense is a stage, not a final philosophy.
Main Themes
Santayana’s treatment of matter and nature is central. Matter, for him, is not a substance known directly but a posit — the principle of existence, characterized by efficacy and indeterminateness. The world of common sense is a construction erected over an underlying flux that can never be fully captured; the categories of thing and cause are instruments of action rather than copies of reality.
The self is treated in the same naturalistic spirit. Santayana rejects the notion of a substantial soul; the self is a concretion of habits, memories, and impulses, a unity achieved in experience rather than given in advance. The psyche is an organization of life, and personal identity is a work of reason rather than a simple datum.
The ideal is the volume’s practical center. Reason, for Santayana, is the perception of the permanent within the flux, and its function is to harmonize impulse into a coherent life. The good is what satisfies impulse harmoniously; the ideal is the imagined perfection of a life. Yet Santayana insists on the natural antagonism and the humility of reason: ideals are generated by impulse and can never be fully realized, and reason must acknowledge its dependence on nature, fortune, and unreasoned desire. The rational life is not a triumph over nature but a working union of impulse and idea.
The volume closes with reflection on truth, understood as the relation between ideas and the objects they intend. Truth is an ideal of thought rather than a simple copy of reality; ideas are true when they successfully guide action and organize experience. Knowledge, for Santayana, rests on an unreflective trust in the existence of a world beyond the immediate flux — a trust that common sense embodies and philosophy must acknowledge.
Throughout, the book’s method is descriptive and literary rather than analytic. Santayana proceeds by reconstructing the phases through which experience must pass in order to become rational, and he writes in a prose rich in metaphor and aphorism. Reason in Common Sense thus serves as the foundation for the whole Life of Reason: it shows how the rational life emerges from the life of impulse and remains rooted in it, and it establishes the naturalistic, developmental standpoint from which the later volumes examine society, religion, art, and science.
Additional Themes and Significance
Santayana’s account of the immediate flux is not a skeptical conclusion but the starting point for a genetic account of intelligence. Pure feeling is an undifferentiated passage; objects, selves, and causes are not simply given but achieved. Reason begins when attention detains a quality, treats it as an essence, and uses it as a sign of something beyond the present. Knowledge is thus continuous with animal adjustment: ideas are instruments of orientation rather than copies of a ready-made world. The distinction between essence and existence is fundamental to the volume—what is intuited is a quality, while what is believed is an existence—and common sense lives by positing existences it never directly possesses.
The book’s treatment of reason is moral as much as cognitive. Reason is not a faculty legislating from outside life; it is the discipline by which competing impulses are represented, compared, and composed into a stable interest. Common sense is reason in its first practical form—a deposit of habits, discriminations, and expectations that makes action possible. It is neither infallible nor merely conventional: it is rational insofar as it organizes experience successfully, and it is revisable insofar as new experience exposes its incoherences. Santayana’s genetic method therefore treats the growth of knowledge as one phase of the growth of a rational life, not as a separate theoretical enterprise.
The volume also develops a naturalistic account of the ideal without collapsing it into fact. Ideals arise from impulse and are tested by their capacity to harmonize a life; they are not arbitrary projections, but neither are they guarantees of cosmic support. Reason’s virtue lies in accepting this double dependence—on the materials of impulse and on the contingencies of nature—while still demanding coherence. The rational life is portrayed as an achievement of balance rather than a conquest of unreason. This gives the book its distinctive tone: sober about limits, but not resigned; critical of common sense, but unwilling to abandon it.
Its significance lies in this integration of epistemology, ethics, and natural history. Reason in Common Sense offers neither a defense of naive realism nor a flight into pure idealism. It interprets common sense as a provisional but indispensable organization of experience, and it interprets reason as the imaginative and practical extension of that organization. By grounding the life of reason in impulse, sign, and action, the volume presents reason as both authoritative and dependent—a power that orders experience without ever escaping the conditions that make it possible.
