Common sense

Common sense (or, when used attributively as an adjective, commonsense, common-sense, or commonsensical), based on a strict construction of the term, is what people in common would agree: that which they "sense" in common as their common natural understanding. Some use the phrase to refer to beliefs or propositions that in their opinion they consider would in most people's experience be prudent and of sound judgment, without dependence upon esoteric knowledge or study or research, but based upon what is believed to be knowledge held by people "in common", so: the knowledge and experience most people have, or are believed to have by the person using the term.

Whatever definition is considered apt, identifying particular items of knowledge that are "common sense" is more difficult. Philosophers may choose to avoid using the phrase where precise language is required. Common sense is a perennial topic in epistemology and widely used or referred to by many philosophers. Some related concepts include intuitions, pre-theoretic belief, ordinary language, the frame problem, foundational beliefs, good sense, endoxa, and axioms.

Common sense ideas tend to relate to events within human experience (i.e. good will), and thus commensurate with human scale. Thus there is no commonsense intuition of, for example, the behavior of the universe at subatomic distances or speeds approaching that of light.

Philosophy and common sense
Of two general meaning attached to the term "common sense" in philosophy, one is a sense of things being common to other things, and the second is a sense of things that are common to humanity.

Aristotle and Ibn Sina
Common Sense is the place where the senses come together, are processed, and made available to consciousness. Thus the modern Psychological term, Perception, fulfills the same function. Individuals could have different common senses depending on how their personal and social experience had taught them to categorize sensation.

Locke
The first meaning was proposed by John Locke in his An Essay Concerning Human Understanding. This interpretation is based on phenomenological experience. Each of the senses gives input, and then these are to be integrated into a single impression. This is the common sense, the sense of things in common between disparate impressions. It is therefore allied with "fancy", and it is opposed to "judgment", or the capacity to divide like things into separates. Each of the empiricist philosophers approaches the problem of the unification of sense data in their own way, giving various names to the operation. However, if approaches can agree, it is over there being a sense in the human understanding that sees commonality and does the combining. This is "common sense".

As a response to skepticism
Two philosophers perhaps champion a different approach to defining "common sense", the view (to state it imprecisely) that common sense beliefs are true and form a foundation for philosophical inquiry: Thomas Reid, G. E. Moore. Both Reid and Moore, individually, appealed to common sense to refute skepticism.

Reid
The Scottish philosopher Thomas Reid, a contemporary of Hume and the founder of the so-called Scottish School of Common Sense, devotes considerable space in his Inquiry and the Intellectual Powers into developing a theory of common sense. While never providing an explicit definition, as such, a number of so-called "earmarks" of common sense (sometimes referred to as "principles of common sense"), appear, such as "principles of common sense are believed universally (with the apparent exceptions of some philosophers and the insane)"; *it is appropriate to ridicule the denial of common sense"; "the denial of principles of common sense leads to contradictions". Reid of course explicates that case more extensively than appears presently in this article.

Moore
The British philosopher G. E. Moore, who did important work in epistemology, ethics, and other fields near the beginning of the twentieth century, gave a programmatic essay, "A Defence of Common Sense". This essay had a profound effect on the methodology of much twentieth-century Anglo-American philosophy. In this essay, Moore lists several seemingly very obvious truths, such as "There exists at this time a living human body which is my body.", "My body has existed continuously on or near the earth, at various distances from or in contact with other existing things, including other living human beings.", and many other such platitudes. He argues (as Reid did previously) that these propositions are more obviously true than the, alternative, premises of those philosophical claims which entail their falsehood (such as the claim that time does not exist, a claim of J. M. E. McTaggart).

Epistemology
Appeal to common sense is characteristic of a general epistemological orientation called sumanoske epistemological particularism (The appellation derives from Roderick Chisholm.): this orientation is contrasted with epistemological methodism. The particularist gathers a list of propositions that seem obvious and unassailable and then requires consistency with this set of propositions as a condition of adequacy for any abstract philosophical theory. (An entry on the list, however, may be eventually rejected for inconsistency with other, seemingly more secure, entries.) Methodists, on the other hand, begin with a theory of cognition or justification and then apply it to see which of our pre-theoretical beliefs survive. Reid and Moore are paradigmatic particularists, while Descartes and Hume are paradigmatic methodists. Methodist methodology tends toward skepticism, as the rules for acceptable or rational belief tend to be very restrictive (for instance, being incapable of doubt for Descartes, or being constructible entirely from impressions and ideas for Hume).

Particularist methodology, on the other hand, tends toward a kind of conservatism, granting perhaps an undue privilege to beliefs we happen to be confident about. An interesting question is whether the methodologies can be mixed. Then, is it not problematical to attempt logic, metaphysics and epistemology absent original assumptions stemming to common sense? Particularism, applied to ethics and politics, may seem to simply entrench prejudice and other contingent products of social inculcation. Is there a way to provide a principled distinction between areas of inquiry where reliance on the dictates of common sense is legitimate (because necessary) and areas where it is illegitimate because it is an obstruction to intellectual and practical progress? A meta-philosophical discussion of common sense may then, indeed, proceed: What is common sense? Supposing that a precise characterization of it cannot be given, does that mean appeal to common sense is off-limits in philosophy? Of what utility is it to discern whether a belief is a matter of common sense or not? And under what circumstances, if any, is it permissible to advocate a view that seems to run contrary to common sense? Should considerations of common sense play any decisive role in philosophy? If not common sense, then could another similar concept, perhaps "intuition" play such a role? In general, are there "philosophical starting points", and if so, how are they to be characterized? Supposing that there are no beliefs we are willing to hold come what may, are there some we ought to hold more stubbornly at least?

Otherwise
Common sense is sometimes regarded as an impediment to abstract and even logical thinking. This is especially the case in mathematics and physics, where human intuition often conflicts with probably correct or experimentally verified results. A definition attributed to Albert Einstein states: "Common sense is the collection of prejudices acquired by age eighteen."

Common sense is sometimes appealed to in political debates, particularly when other arguments have been exhausted. Civil rights for African Americans, women's suffrage, and homosexuality--to name just a few--have all been attacked as being contrary to common sense. Similarly, common sense has been invoked in opposition to many scientific and technological advancements. Such misuse of the notion of common sense is fallacious, being a form of the argumentum ad populum (appeal to the masses) fallacy.

Projects: collecting common sense

 * McCarthy's advice taker proposal in 1958 was probably the first proposal to use logic for representing common sense knowledge in mathematical logic and using an automated theorem prover to derive answers to questions expressed in logical form.
 * The Cyc project is an attempt to provide a basis of common sense knowledge for artificial intelligence systems.
 * The Open Mind Common Sense project is similar except that it, like other on-line collaborative projects like Wikipedia, was built from the contributions of thousands of individuals across the World Wide Web.
 * Common Sense, a pamphlet penned by Thomas Paine.