War and civil unrest became increasingly prominent in European consciousness after the Protestant Reformation. Paradoxes became described in militaristic terms. Rationalists defended themselves from atop a citadel of mathematics and pure reason. The empiricists retreated to the growing fortress of physics. Thomas Reid takes the battle out to the plains of common sense.
Reid prefaces his Inquiry into the Human Mind: On the Principles of Common Sense by remarking,
that I never thought of calling into question the principles commonly received with regard to the human understanding, until the “Treatise of Human Nature” was published in the year 1739. The ingenious author of that treatise upon the principles of Locke—who is not sceptic—hath built a system of scepticism, which leaves no ground to believe any one thing rather than its contrary. His reasoning appeared to me to be just; there was, therefore, a necessity to call in question the principles upon which it was founded, or to admit the conclusion.
(1764, 1)
Reid actually traces the principles to Descartes. If you believe that you directly perceive only ideas, then any beliefs you have about things outside this private realm must be justified by an inference. If you can show that a proposition cannot be proved from premises about our ideas, you have shown that it is not held on rational grounds.
Descartes characterized ideas as supremely knowable. They have no hidden properties. Ideas are exactly as they appear to be. They set the standard for certainty. Truths about ideas are Archimedean points that allow reason to pry out myths from the otherwise immovable earth of common sense. Given Descartes’s Way of Ideas, reason operates as a tribunal that oversees the deliverances of all other faculties. Reid wrote:
The defects and blemishes in the received philosophy concerning the mind, which have most exposed it to the contempt and ridicule of sensible men, have chiefly been owing to this—that the votaries of this Philosophy, from a natural prejudice in her favour, have endeavored to extend her jurisdiction beyond its just limits, and to call to her bar the dictates of Common Sense. But these decline this jurisdiction; they disdain the trial of reasoning, and disown its authority; they neither claim its aid nor dread its attacks.
(1764, I, iv)
Reid’s project is to restore the dignity of philosophy. Hume has inadvertently demonstrated the absurdity of the way of ideas. Reid’s negative task is to diagnose why this doctrine seems so attractive and why it fails. His positive task is to replace the Way of Ideas with an alternative theory of perception and knowledge that conforms with common sense. Although I am a convert to Reid’s causal theory of perception, I shall concentrate on his account of common sense.
Reid characterizes common sense as a body of beliefs that issues from a faculty that nearly all human beings exercise daily. Since the source is the same, common-sense beliefs are universal and coeval with the origin of mankind. Unlike science, common sense is immutable and so does not make progress. Aside from infants and lunatics, there is massive agreement about our environment and each other. These propositions are compulsively believed because they are essential to health and safety. Since children also need to survive, common-sense beliefs “appear so early in the minds of men that they cannot be the effect of education or of false reasoning.” They are reflected in the distinctions present in all natural languages: male/female, substance/quality, active/passive, past/present/future, etc.
The universality of common-sense beliefs make them too trite to articulate. However, this does not stop them from having the status of first principles. Common-sense beliefs are self-evident. There is no searching for evidence, no consulting of authorities, no chains of deduction. The negations of common-sense beliefs are immediately recognized as false:
We may observe that opinions which contradict first principles, are distinguished, from other errors, by this:—That they are not only false but absurd; and, to discountenance absurdity, Nature hath given us a particular emotion—to wit, that of ridicule—which seems intended for this very purpose of putting out of countenance what is absurd, either in opinion or practice.
(1764, VI, iv)
The emotion fitted to paradox is amusement. A conclusion that runs contrary to common sense would be dangerous to take seriously.
Given the compulsive nature of common sense, people who oppose it generally lapse into inconsistency. General doubts are never consummated with particulars. If you stroll with a skeptic, he will deny that he is justified in believing that he is approaching a post. But he will gingerly walk around it. This gives him away as a hypocrite. Thus, paradoxes often provide a secondary source of amusement—the conflict between the paradox-monger’s words and deeds.
Is this argumentum ad hominem? Yes, says Reid, but it is a “good ad hominem, if it can be shewn that a first principle which a man rejects, stands upon the same footing with others which he admits: for, when this is the case, he must be guilty of an inconsistency who holds the one and rejects the other.” (1764, VI, iv)
The judgments of common sense are overlapping axioms from which reason can prove theorems that are not self-evident. Reid believes that these axioms are consistent with each other. Thus, he disagrees with those who think some paradoxes are built from internal conflicts within common sense. Reid also rejects Hume’s frequent diagnosis of the paradoxes as arising from a conflict between reason and common sense. The job of common sense is to judge what is self-evident. The job of reason is to draw conclusions that are not self-evident from those that are. Therefore, reason must always coincide with common sense.
Geometers prefer that axioms be independent of each other. This helps reduce the number of axioms. One price of this economy is that deductions tend to be longer. Common sense needs to be fast, so it has a large number of axioms that are organically connected to each other. When it comes to common sense, we cannot pick and choose. We must accept the entire root system.
Reid admits that there is vagueness about the boundaries of common sense. He does not attempt to exhaustively list all of its principles. However, he specifies the principles pertinent to philosophy. Many of these are contingent truths. Reid tends to couch them as premises that can be readily marshaled against Hume’s skepticism:
1. That the thoughts of which I am conscious are thoughts of a being which I call MYSELF, my MIND, my PERSON.
2. That those things did really happen which I distinctly remember.
3. That we have some degree of power over our actions, and the determinations of our will.
4. That there is life and intelligence in our fellow men with whom we converse.
5. That there is a certain regard due to human testimony in matters of fact, and even to human authority in matters of opinion.
6. That, in the phaenomena of nature, what is to be, will probably be like what has been in similar circumstances.
Other principles of common sense concern necessary truths. Some concern grammar, such as, Every complete sentence must have a verb. Yet others concern logic: every proposition is either true or false; none is both truth and false; circular reasoning proves nothing; whatever is affirmed of the genus may be affirmed of the species. Hume had claimed that we cannot form any idea of geometrical figure (such as a straight line) which is not a copy of an earlier impression. Reid counters with common-sense geometry.
Reid did not forget how Hume got his foot in the door of ethics by noting that there is no arguing over taste. Reid confronts Hume at the top of this slippery slope with first principles concern matters of taste. He thinks judgments of beauty can be rational and true. Morality also has first principles; for example, no one is to be blamed for what he has no power to hinder. Reid resists Hume’s view that moral judgments express feelings rather than judgments.
Reid’s list also includes metaphysical first principles: for instance, thoughts must have a subject (a thinker) and anything that begins to exist must have a cause. Defenders of the design argument for the existence of God will find uses for this principle: “That design and intelligence in the cause may be inferred, with certainty, from marks or signs of it in the effect.” The universe is so orderly that it is readily described as a giant, intricate machine. Where there is an artifact, it is reasonable to infer a maker of powers and foresight proportional to the effect.
Reid’s common sense looks like an impression left by Hume; concave where Hume is convex, convex where Hume is concave. One explanation is that common sense is reactive. We do not bother to defend (or even think about) the proposition that the future resembles the past until David Hume formulates the problem of induction. Paradoxes illuminate common sense by provoking bits of it into consciousness. As more paradoxes are discovered, more of common sense becomes visible. Without a provocateur, common sense is faceless.
Like Reid, Sydney Smith was a Scottish clergyman. Smith helped found the Edinburgh Review. One day Smith and a friend encountered two women screaming insults at each other from second-story windows at the opposite sides of a narrow Edinburgh street. “Those two will never resolve their differences,” remarked Smith, “They are speaking from separate premises.” (Fadiman 1985, 514)
Reid thought debate with skeptics was futile because of a lack of shared premises. The first principle of common sense is that the natural faculties are not fallacious. Any proof of this principle would be circular because reason is itself a faculty. If anyone were to reject this principle, “it would be impossible by argument to beat him out of his stronghold; and he must even be left to enjoy his scepticism.” (1764, VI, 5)
Reid is too pessimistic. Incompatible premises can imply the same conclusion. When my watch says it is 1:10 and yours says it is 1:15, they conflict. Yet each entail that it is past 1:00. You can change your adversary’s conclusion by reasoning from his premises and his inference rules. In 1684, the British playwright Nathaniel Lee was confined in the London asylum Bedlam. A friend, who had heard Lee was suffering one of his bouts of insanity, visited him. To his relief, he found Lee calm and reasonable. Lee took his friend on a tour around the asylum. His friend’s hopes soared. When they eventually reached the roof of the asylum, Lee suddenly gripped his friend’s arm and excitedly exclaimed, “Let us immortalize ourselves; let us leap down this moment!” Lee’s friend coolly responded: “Any man could leap down, so we should not immortalize ourselves that way. But let us go down and try if we can leap up.” Nathaniel Lee was delighted by this counterproposal and ran down the stairs to see if he could put it into practice. (Fadiman 1985, 348)
Although Reid sometimes harshly characterizes his adversaries as “metaphysical lunatics,” he distinguishes them from the institutionalized variety. Metaphysical lunatics only have fleeting departures from common sense.
We are born under a necessity of trusting to our reasoning and judging powers; and a real belief of their being fallacious cannot be maintained for any considerable time by the greatest Sceptic, because it is doing violence to our constitution. It is like a man’s walking upon his hands, a feat which some men upon occasion can exhibit; but no man ever made a long journey in this manner. Cease to admire his dexterity, and he will, like other men, betake himself to his legs.
(1785, VI, 5)
Reid compared the power of reason to walking. It is acquired and sustained by exercise. Nature prompts our first steps. “After repeated efforts, much stumbling, and many falls, we learn to walk; and it is in a similar manner that we learn to reason.” Philosophers tend to arbitrarily elevate reason above the other faculties of perception and common sense. Reid thinks reason can never override common sense:
The sceptic asks me, Why do you believe the existence of the external object which you perceive? This belief, sir, is none of my manufacture; it came from the mint of Nature; it bears her image and superscription; and, if it is not right, the fault is not mine: I even took it upon trust, and without suspicion. Reason, says the sceptic, is the only judge of truth, and you ought to throw off every opinion and every belief that is not grounded on reason. Why, sir, should I believe the faculty of reason more than that of perception?—they came both out of the same shop, and were made by the same artist; and if he puts one piece of false ware into my hands, what should hinder him from putting another?
(1764, VI, xx)
Philosophers who follow the Way of Ideas are guilty of a double standard. They meekly accept the deliverances of introspection, yet they eye the deliverances of perception and memory with suspicion. In truth, the deliverances of introspection seem more doubtful. We have trouble attending to the workings of our own minds. After all, sensations are designed to aid perception. They are not designed to be objects of perception in their own right.
Socrates said that we should follow the argument wherever it leads. Descartes supports Socrates with an analogy. If a traveler is lost in a forest, then he should continue to walk as straight as he can in one direction. The traveler may not end up where he wished, but he will probably be better off than in the middle of the forest.
True, when people are bereft of landmarks, they tend to walk in circles. But is philosophy typically a journey with no clues along the way? At the very least, says Reid, philosophers can use information about where they end up to assess the correctness of their route: “A traveller of good judgment may mistake his way, and be unawares led into a wrong track; and, while the road is fair before him, he may go on without suspicion and be followed by others; but when it ends in a coal-pit, it requires no great judgment to know that he hath gone wrong.” (1764, introduction, VIII) Any conflict with common sense is a sure sign that there is a mistake somewhere. We do not need to wait for a diagnosis of the error before rejecting the argument.
In a letter to Hugh Blair dated July 4, 1762, Hume objects to Reid’s oversophistication of common sense:
The Author supposes, that the Vulgar do not believe the sensible Qualities of Heat, Smell, sound, & probably Colour to be really in the Bodies, but only their Causes or something capable of producing them in the Mind. But this is imagining the Vulgar to be Philosophers & Corpuscularians from the Infancy. You know what pains it cost Malebranche & Locke to establish that Principle. There are but obscure Traces of it among the Ancients viz in the Epicurean School. The Peripatetics maintained opposite Principles. And indeed Philosophy scarce ever advances a greater Paradox in the Eyes of the People, than when it affirms that Snow is neither cold nor white: Fire hot nor red.
(Aberdeen University Library MS 2814/139)
Subsequent philosophers share Hume’s suspicion that Reid gerrymanders the constituency of common sense to ensure that it is never defeated. The American pragmatist C. S. Peirce (1839-1914) thought that common sense courts this illicit support because it is so vague. It is common sense that there is some order in nature, but only more specific descendants precisifications of that amorphous conviction are open to refutation.
Peirce agrees with Reid that common-sense beliefs are indubitable. Hume only had “paper doubts.” Peirce characterized strong thinkers as great breath-holders. Holding your breath against a belief is not doubting it. But unlike Reid, Peirce denies that indubitability implies truth. As a fallibilist, Peirce thinks any of our beliefs could be mistaken. Still, Peirce does not think all of our beliefs could be false.
Henry Sidgwick maintained that science and philosophy “continually at once corrects and confirms crude Common Sense.” (1905, 425) This great mass of ore must be smelted by philosophers to remove “inadvertencies, confusions, and contradictions.” (1905, 428) His Methods of Ethics (1874) shows how the morality of common sense incorporates awkward compromises between conflicting ideas, how it trails off into vagueness and vicious incompleteness. He presents utilitarianism as a moral theory that conservatively streamlines common sense.
Many philosophers believe common sense has a self-amendment clause. G. F. Stout (1860–1944) conceived of common sense as less a matter of specific beliefs and more a matter of general tendencies to form beliefs. He viewed science and philosophy as polishing away the animistic rough edges of common sense (“the tendency to find Mind in Nature generally”). Stout thought common sense always has the last word because philosophical and scientific challenges only succeed when they use common sense to overcome the presumption not to change common sense.
Bertrand Russell denies that common sense must always be accommodated. He quipped “Common sense implies physics and physics refutes common sense.” As vague as common sense is, it still makes falsifiable claims.
The most famous common-sense philosopher of the twentieth century, G. E. Moore, admitted that common sense underestimates the distance from the earth to other heavenly bodies. G. E. Moore makes no attempt to define common sense but he is generous with examples: the earth has existed for many years past; inhabitants of the earth have been in contact with one another; they have also been at various distances from each other; and all this is common knowledge. As tame as these truisms may seem, philosophers propose theses that conflict with them. Parmenides did deny the reality of time and this conflicts with the statement, The earth has existed for many years.
Moore’s specimen box also contains propositions that must be expressed with the demonstratives here, now, and that. In his lecture “A Proof of the External World,” Moore held up one hand to support the premise “Here is a hand,” then another hand in support of “And here is another,” and concluded “Therefore, there are at least two material things.” Moore refutes philosophical theses by bringing the abstract into unadorned conflict with the concrete. This style of argument is backed by a principle of weighted certainties. He thought the propositions of common sense were far more evident than the philosophical premises used by idealists and skeptics. So even if common sense is fallible, philosophy cannot hope to overturn it.
This special restriction on philosophy is suspicious in light of Moore’s concession that astronomy has overturned common-sense beliefs about the distance to the stars. There is ample historical evidence that parts of philosophy develop into science. If philosophy leads to science and science overturns common sense, then philosophy must at least have an indirect ability to overturn common sense.
Moore also neglects the extent to which philosophers prompt a change of mind by pointing out conflicts (and convergences) that are independent of their own philosophies. Logicians are especially fond of being neutral commentators who point out that the claimants for our credence are operating at cross-purposes.
Computer scientists initially tried to manufacture intelligence by getting computers to perform tasks that human beings find intellectually challenging: calculating missile trajectories, breaking codes, winning at chess. Progress was rapid after the first electronic computers were developed in World War II. The achievements of these electronic brains were humbling: problems that are hard for people are easy for computers. Was there anything computers could not do?
Computers do have trouble coping with combinatorial explosions. Consider a traveling salesman who wants to know the shortest route connecting a number of cities. As the number of cities increases, the number of possible routes grows exponentially. A computer that is programmed to solve the problem by brute force will rust out before examining all the possible paths that exist between 100 cities. Computer scientists respond by giving up the goal of finding the shortest route in favor of the more tractable goal of probably finding a route that is close to the shortest. This scaled-back objective allows the computer to focus on promising routes.
In 1969, John McCarthy and Patrick Hayes published their discovery of a general combinatorial explosion: the frame problem. How can a computer update knowledge of a changing situation? The objects and properties that make up a situation are interdependent. Thus, the number of possible side effects grows exponentially with the number of objects and the number of properties they may possess. Suppose my plan is to illuminate a room by walking over to the light switch and flipping it on. How do I know that my first step will not break the light bulb? How do I know that my second step will not make the light switch scurry to a new location on the wall? These are silly questions. Their philosophical air is due to an absence of common sense. But unlike human beings, computers do not develop common sense on their own. To solve the frame problem, researchers must artificially instill common sense. They must introduce “frame axioms” analogous to Reid’s first principles. The computer scientists are guided by the sort of paradoxes that Reid relies upon in his pioneering efforts.
Psychologists who study common sense have been influenced by both computers and evolutionary theory. Reid thought common sense was created by God, so Reid could easily explain its perfections. The hypothesis of divine design has much more trouble accounting for imperfections. Accordingly, Reid is reluctant to admit any flaws in common sense.
The evolutionary account of common sense easily explains the imperfections of common sense but has more trouble accounting for its perfections. If common sense is an adaptive trait, then we cannot depend on God’s foresight.
Evolution cannot take one step back to take two steps forward. Natural selection develops traits short-sightedly, with each step forward requiring an immediate payoff. It is a blind hill-climber. In a terrain with many hills, it will arrive at a summit but almost certainly not the highest summit. For once natural selection climbs to the top of a small hill, the rule “Always go up!” vetoes a precondition for moving to a higher hill. Common sense is a collection of local optima. Little wonder that people, with the benefit of foresight, can artificially do better than common sense.
Evolution cannot afford to put all its eggs in one basket. Common sense must be a diversified collection of judgmental tendencies. One part must be permitted to fail without a catastrophic collapse of the corporate body. If God had designed common sense in one omniscient swoop, then it could be the sort of all-or-nothing package Reid envisaged. But common sense must have more of the modular character that computer scientists will inevitably confer on their common-sense computers (if the frame problem is soluble).
Reid says that only infants and lunatics lack common sense. The contrasts are more nuanced than this. Developmental psychologists have shown that children develop common sense in stages. For instance, naive physics is acquired before naive psychology. The ability to attribute desires matures before the ability to attribute beliefs. Three-year-old children operate under the assumption that others believe what they do. Consequently, they have trouble attributing false beliefs.
Mental disorders are also more diverse than Reid assumed. The mental disorder of autism suggests that the acquisition of naive physics is not invariably followed by the acquisition of naive psychology. Other mental disorders suggest that common sense is composed of modules that can be selectively incapacitated. Philosophers have an interest in these diseases of common sense; they show paradoxes operating in a genuinely pathological manner.
Developmental psychology and abnormal psychology are “philosophical” areas of psychology. Like philosophy, they illuminate common sense by studying what happens when common sense fails to operate.