Common Sense: Meaning, Philosophy & Wisdom

Meaning and Definition

Common sense is the shared faculty of sound practical judgment. In its everyday meaning, common sense names the unreflective wisdom that ordinary people deploy to navigate the world: the knowledge that fire burns, that the sun will rise tomorrow, that you should look before you leap. It is the body of basic beliefs and reasoning capacities that we rely on without needing to justify them, the practical intelligence that allows us to function without a philosopher looking over our shoulder. "It is just common sense," we say, and what we mean is that the matter is so obvious, so widely shared, so basic to competent functioning that it should not require argument.

The philosophical concept of common sense is both more precise and more contested than the everyday one. Philosophers have used the term in at least two distinct ways. First, common sense can name a universal rational faculty — the "good sense" (bona mens) that Descartes invokes at the opening of the Discourse on the Method, the capacity for reasoned judgment that is "the best distributed thing in the world," present in everyone and differing only in how well it is used. On this view, common sense is the shared foundation of rational inquiry, the capacity that makes philosophy possible. Second, common sense can name a body of settled beliefs — the convictions that ordinary people hold about the world, themselves, and other minds, which Thomas Reid and the Scottish Common Sense school treated as the proper starting point and test of philosophical theorizing. On this view, common sense is not just a faculty but a set of commitments that philosophy ignores at its peril.

The tension between these two senses runs through the whole philosophical history of the concept. If common sense is a universal rational faculty, then it is the ally of philosophy — the shared capacity that disciplined inquiry refines and extends. If common sense is a body of settled beliefs, then it can be both the foundation of philosophy and its critic — the touchstone against which philosophical theories must be tested, and the voice that says "but everyone knows that" when a theory strays too far from what ordinary judgment can recognize. The question of whether common sense is a reliable guide or a seductive prejudice is one of the standing questions of epistemology.

What makes common sense philosophically interesting is precisely its ambiguous status. It is both the most ordinary thing in the world — the judgments we make without thinking — and a sophisticated philosophical concept that has been used to ground knowledge, to criticize skepticism, and to expose the limits of theoretical reasoning. The wisdom of common sense is not the wisdom of the expert but the wisdom of the competent participant in shared human life, and the question of how much weight that wisdom deserves is one that every serious thinker must confront.

Philosophical Perspectives

Descartes and the Universal Faculty of Good Sense

Descartes gives common sense its first modern philosophical formulation, though in a sense quite different from what later philosophers would mean by the term. In the opening of the Discourse on the Method (1637), Descartes famously declares that "good sense is the best distributed thing in the world," because everyone thinks himself so well endowed with it that even those who are hardest to satisfy in every other respect do not usually want more of it than they already have. By "good sense" (le bon sens, the Latin bona mens), Descartes means the universal rational faculty — the capacity to distinguish truth from falsehood — that is present in every human mind. The Stanford Encyclopedia of Philosophy notes that Descartes treats this faculty as the natural foundation of knowledge, the shared capacity that makes inquiry possible.

For Descartes, the problem is not that people lack good sense but that they fail to use it well. The differences between a great mind and an ordinary one are not in the raw capacity for reason but in the method of its application. The person who reasons carefully and systematically — who follows the rules of method, who doubts what is not clear, who proceeds step by step — will achieve knowledge that the person of equal natural capacity but undisciplined method will never reach. Common sense, in Descartes' sense, is not a body of beliefs but a capacity, and its value depends on how it is exercised. This is a strikingly democratic view — reason is available to all — combined with a demanding discipline — but few use it properly.

The Cartesian common sense is thus both the starting point and the thing that must be transcended. Philosophy begins with the universal faculty of reason, but it cannot rest with the ordinary deliverances of that faculty, which are mixed with prejudice, habit, and error. The method of doubt is designed to strip away everything that common sense accepts on insufficient grounds, so that the mind is left only with what is clear and distinct. In this sense, Descartes both honors and distrusts common sense: he honors it as the shared capacity that makes knowledge possible, and he distrusts its ordinary deliverances as unreliable until they have been subjected to methodical scrutiny.

Thomas Reid and the Scottish Common Sense School

The most sustained philosophical defense of common sense comes from Thomas Reid (1710-1796) and the Scottish Common Sense school, which arose as a response to the skepticism of David Hume. Hume's empiricism had led him to argue that we have no rational justification for some of our most basic beliefs — the belief in an external world, the belief in causal connection, the belief in a continuing self. These beliefs, Hume argued, are not grounded in reason or experience but in custom and habit. The skeptical conclusion seemed to follow: if our most fundamental beliefs lack rational justification, then knowledge itself is in trouble.

Reid's response was radical. He argued that Hume's skepticism was not a discovery about the weakness of human knowledge but a reductio ad absurdum of the philosophical assumptions that produced it. The empiricist theory of ideas — the view that the mind is directly aware only of its own ideas or impressions, and must infer the existence of an external world from them — was, Reid argued, the source of the problem. If you assume that the mind is enclosed in a veil of ideas, then you will never be able to justify the belief that there is a world beyond the veil. But the assumption itself is false. We do not perceive ideas; we perceive the world. And our belief in the world is not an inference from something more basic but a primitive, unavoidable conviction that is part of the constitution of the human mind.

Reid called these primitive convictions "first principles" or "principles of common sense," and he argued that they are the proper foundation of all knowledge. The Internet Encyclopedia of Philosophy explains that Reid's common sense philosophy treats these first principles as self-evident — not in the sense that they can be proven, but in the sense that they cannot be reasonably denied, because all reasoning and all inquiry presuppose them. You cannot argue against the reliability of your faculties without using your faculties; you cannot doubt the existence of an external world without assuming it in the very act of doubting. Common sense, on Reid's view, is not a set of popular opinions but the set of beliefs that are necessarily presupposed by all rational inquiry — the bedrock that philosophy cannot dig beneath because it must stand on it.

The Scottish Common Sense school had enormous influence in the eighteenth and nineteenth centuries, particularly in Scotland and America, where it shaped the teaching of philosophy for generations. Its influence declined in the twentieth century with the rise of analytic philosophy, but its central insight — that some beliefs are properly basic, not because they are proven but because they are the unavoidable presuppositions of all inquiry — has been revived in contemporary epistemology, particularly in the work of philosophers who defend a form of foundationalism or who argue that common sense beliefs carry a default entitlement that can only be defeated by specific reasons, not by general skeptical arguments.

Common Sense Against Philosophy: The Critical Dimension

The concept of common sense has always had a critical as well as a foundational role. When a philosopher arrives at a conclusion that contradicts what everyone believes — that motion is impossible, that the external world does not exist, that time is unreal — common sense raises an objection. The question is whether this objection is philosophically significant or merely complacent. Is common sense a legitimate critic of philosophy, or is it just the voice of unexamined prejudice?

Reid's answer is that common sense is a legitimate critic when the philosophical conclusion contradicts first principles — the beliefs that are necessarily presupposed by all inquiry. A philosophical argument that concludes that there is no external world is not just surprising; it is self-undermining, because the argument itself presupposes the existence of the world (the existence of the philosopher, the words of the argument, the audience to whom it is addressed). In such cases, the proper response is not to accept the conclusion but to find the error in the premises. But common sense is not a legitimate critic when it rejects a conclusion merely because it is unfamiliar. Many true conclusions — the Earth moves around the Sun, matter is mostly empty space, time is relative — contradict what common sense once believed, and in these cases common sense was simply wrong. The challenge is to distinguish the cases where common sense is the bedrock of inquiry from the cases where it is the obstacle to discovery.

This distinction is the heart of the philosophical problem of common sense. If common sense is always right, then philosophy can never discover anything surprising, and inquiry is reduced to the articulation of what we already believe. If common sense is always suspect, then we have no foundation, and skepticism threatens. The most defensible position, which Reid himself seems to hold, is that common sense provides a set of defeasible defaults — beliefs that we are entitled to hold in the absence of defeating reasons, but that can be revised when genuine evidence requires it. Common sense is the starting point, not the终点; it is what we believe until we have reason to believe otherwise.

Modern Reflection

The concept of common sense remains live in contemporary philosophy, though it has been transformed by the analytic and naturalistic turns. G.E. Moore's "Defense of Common Sense" (1925) revived the Reid-style appeal to common sense as a response to skepticism. Moore argued that we are more certain of common sense beliefs — "Here is a hand," "The Earth has existed for many years" — than we are of any philosophical argument that would deny them, and that the proper response to skepticism is therefore to trust the beliefs and reject the arguments. Moore's defense has been enormously influential, though it has also been criticized as question-begging — as assuming the very thing that the skeptic challenges.

Contemporary epistemology has developed more sophisticated versions of the common sense position. The "default and challenge" model, associated with philosophers like Timothy Williamson and others, holds that common sense beliefs carry a default epistemic status: we are entitled to hold them without evidence, but we must give them up if a specific challenge defeats them. This model preserves the Reid insight that common sense is the starting point of inquiry while acknowledging that common sense can be wrong and that scientific discovery can overturn even deeply held convictions. The debate turns on how strong the default is — how much defeater-force is needed to overturn a common sense belief — and on whether the model can be made precise enough to be useful.

The concept of common sense also plays a role in contemporary political and social philosophy. Appeals to common sense are often used to criticize expert consensus, institutional authority, and theoretical complexity, and the question of whether common sense is a democratic virtue or a populist danger has become politically charged. Philosophically, the issue is the same one that Reid faced: common sense is the shared judgment of ordinary people, and the question is how much authority that judgment deserves in matters that exceed ordinary experience. The answer cannot be simple — neither the uncritical glorification of common sense nor its wholesale dismissal is defensible — and the philosophical tradition offers resources for thinking through the complexity.

Related Concepts

• Knowledge — Common sense is the foundation on which knowledge rests, or the critic that tests philosophical claims about knowledge. The debate over common sense is ultimately a debate about the structure and justification of knowledge.
• Truth — Common sense claims to deliver truths so basic that they cannot be doubted without self-contradiction. The philosophical question is whether these common sense truths are genuinely self-evident or merely deeply ingrained habits.
• Reason — Common sense is the universal rational faculty that Descartes identified, or the body of settled beliefs that Reid defended. In both cases, it is connected to the capacity for sound judgment that philosophy seeks to refine.

Learning Path

1. Begin with Knowledge to understand the epistemological framework within which common sense operates — as either the foundation of knowledge or its critical test.
2. Study Truth to explore the relationship between common sense beliefs and truth, and to see why philosophers have disagreed about whether common sense is a reliable guide.
3. Examine Descartes for the account of good sense (bona mens) as the universal rational faculty — the shared capacity for reasoned judgment that makes philosophy possible.
4. Read Thomas Reid's An Inquiry into the Human Mind (1764) and Essays on the Intellectual Powers of Man (1785) for the Scottish Common Sense defense of first principles as the unavoidable presuppositions of all inquiry.
5. Reflect on the role of common sense in your own thinking, and consider how the wisdom collected in Understanding Reality applies to the distinction between common sense as bedrock and common sense as obstacle.

Sources

• Stanford Encyclopedia of Philosophy, Thomas Reid.
• Stanford Encyclopedia of Philosophy, Descartes.
• Internet Encyclopedia of Philosophy, Common Sense.
• Thomas Reid, An Inquiry into the Human Mind on the Principles of Common Sense (Edinburgh: Edinburgh University Press, 1997).