My senior thesis at Gutenberg College was about how to judge narrative: How do we determine whether a story is good or not? I pursued this question because in a school full of smart, opinionated people, I felt that some of the movies and books I liked were under constant attack, but these same smart, opinionated people were unable to tell me why they did not like my fare. I concluded that even articulate people sometimes have tacit criteria, which, once discovered, were not the same criteria I valued, and thus I was free to like the things I do. But literary criticism is what we might call a secondary order question. What happens when very smart, opinionated people disagree with me about primary order questions? What if they are emphatic that I have no right to my beliefs about God, life, and death unless I can convince them of my beliefs? This is significant, not only because it affects the questions about God, life, and death but also because it presupposes an answer to the question of how we know what we know. It supposes that unless we have an indubitable basis for knowledge, we have no right to knowledge. To answer such an assault on our beliefs, we must seek to understand both why such people have the opinions they do and if indubitable knowledge is the same as reasonable knowledge.

Scottish philosopher Thomas Reid (1710–1796) argued that the philosophers of his age conflated indubitable knowledge and reasonable knowledge and that his theory of Common Sense was a reasonable alternative to the bases of knowledge they proposed. While Reid’s project was to counter the prevalent theories of his time, during the era we have come to know as the Enlightenment, his theory of Common Sense is just as relevant today because the arguments of the Enlightenment have become more than merely academic; they comprise the backcloth of all the postmodern thought in which our culture is steeped. Before looking at Reid’s argument, then, we must understand a little about the Enlightenment and its influence.

The Enlightenment in the seventeenth and eighteenth centuries was a movement in large part reacting to both the Protestant Reformation and the Copernican Revolution in the sixteenth. The Reformation had unseated Catholic authority, and the Copernican Revolution the authority of Greek science. As such, the authoritarian structures of the Middle Ages were no longer viable. Furthermore, the Thirty Years War (1618–1648), a conflict between Protestants and Catholics, obscured whether Christianity had any claim to truth. Major questions were thus facing the Enlightenment philosophers, and three major answers, or impulses, to these questions came to predominate: the empiricist impulse, the scientific impulse, and the rationalistic impulse. These impulses are not necessarily separate in any one thinker, though each impulse deals with a separate question or problem.

The empiricist impulse resolves to avoid any metaphysical speculation. The Thirty-Years War appeared to have demonstrated that no Christian, Protestant or otherwise, had any claim to truth and that all Christianity relied on the rampant metaphysical speculation and naïveté that would be necessary to believe in the miracles recorded in the Bible. Furthermore, until Kepler proved otherwise, even the Copernicans had believed in circular planetary orbits, the circle being a more perfect shape in the Greek mind, which to the empiricist impulse was arbitrary metaphysical hogwash. If our notions of the divine or the perfect can lead us away from truth, what validity do they have?

The scientific impulse aims to avoid subjective perspective in favor of compiling and evaluating objective data. Like the empiricist impulse, the scientific impulse arose in response to the Copernican Revolution, from the fact that the observationally obvious geocentric model—the sun, to this day, looks like it is moving around the earth—proved incorrect. If our perspective causes us to misunderstand the universe, we must find a better perspective. Unfortunately, we are all stuck in more or less the same place (on earth), so what we must do is find that data which is valid from any perspective. The scientific impulse, therefore, only pronounces judgment on any truth-claim once enough data has been collected.

The rationalistic impulse, unlike the empiricist and scientific impulses, rejects the senses as a valid means to truth. The Copernican Revolution showed that sense experience incorrectly tells us the sun goes around the earth. And sense information is questionable, for example, in some vivid dreams, where being awake or asleep is hard to tell. If our senses are so easy to fool, what credence can we give to them? Any truth, the rationalistic impulse argues, will therefore come from careful reflection in the mind.

The three Enlightenment impulses shared two things in common: they rejected authority in favor of individual insight, and they were all searching for an indubitable basis for knowledge. At first blush, such a basis seems important. If we can doubt the simplest of beliefs—my senses are giving me reliable information; I exist—then how can we hope to answer the important questions of how to live life, deal with death, and know if there is a God? What right do we have to believe something unless we first prove it true? Reid realized that the emerging desire for an indubitable basis for knowledge was problematic and that the task of finding such a basis impossible.

The problem, as Reid saw it, is that all human beings assume certain foundational beliefs and possess intrinsic faculties that they must rely on but cannot prove. These foundational beliefs and faculties comprise what he calls “Common Sense,” and he argues that every man, unless he is mad, must use it. Reid does not mean by Common Sense a shared culture but rather the basic wiring of the machine that is the human mind. “I exist” is an example of a foundational belief. Every man, unless he is pretending otherwise or out of his mind, cannot help but act as if he exists. Yet, he cannot prove this fact by logical arguments, and the cure for someone who does not believe he exists is not logical arguments. Examples of faculties would be memory and sense of smell.

Part of Reid’s brilliance is that he was discussing concepts so new that no language existed for them, and so he does a lot of work with a simple vocabulary. If Freud had come along, Reid might have said that Common Sense was comprised of all those unconscious processes that we rely on every day. If Reid had been around in our century, he might have compared Common Sense to the programming that allows a computer to figure out how to handle other programming. While Reid said that philosophers have asked too much of philosophy, if he had known philosopher/scientist Michael Polanyi’s (1891–1976) terminology, he might have said that philosophers have asked too much of articulate knowledge. However else Reid might have described it, all philosophers, following what they perceive to be the most logical of arguments, use Common Sense.

While Reid himself is often classified with the empiricists, he recognized that while empiricism was valuable, the empiricist impulse that repudiates metaphysics was dangerous. Though he never said it outright, Reid’s project, in part, was to justify belief in God. The empiricist impulse, however, takes God off the table a priori; but although God is not within direct experience, Reid thought believing in God’s existence is not unreasonable.

In Reid’s mind, the most dangerous advocate of the empiricist impulse was David Hume (1711-1776), who theorized that the only things human beings can know for sure are sense experiences (“impressions”) and other non-sensational experiences, such as emotions and memories (“ideas”). This line of thinking followed to its logical conclusions erases, among other things, the self, cause and effect, and God. Furthermore, Hume argued that the only sound philosophy was that which assumed all his premises. If someone argued with him on different premises, that person was not taking the Enlightenment project seriously. But if one is powerless even to admit the reality of cause and effect, how can one prove the existence of God?

Reid argued that such a perspective as Hume’s ignores that the Emperor is wearing no clothes. Reid pities the Enlightenment philosopher who feels compelled to provide adamantine proofs, which compulsion, he notes with irony, is highly metaphysical. If Hume’s system eliminates the self, what is receiving the impressions? Can a thought be had without a thinker, or a perception without a perceiver? What is left of a theory that throws away cause and effect? The empiricist philosopher put requirements on himself that no man requires in real life. If, said Reid, enlightened philosophy is going to impose such limits on man, then he would rather be vulgar. Until philosophy is freed from these requirements, he argued, it will be absurd.

Reid also took issue with the scientific impulse. He argued that it does not take into account how human beings actually relate to the world. To the scientist, the senses bring in raw data which the mind then interprets. Reid argued, however, that since human beings see in three dimensions, the mind is already interpreting data before we can perceive it. Furthermore, the desire to secure objective knowledge has the side effect of eliminating the importance of individual perspectives. The scientist, Reid argued, assumes he can take the observer out of the observing, which, as we saw with Hume, is an absurd mistake. Therefore, any science (not driven by the scientific impulse, mind you) must take the individual perceiver into account. Reid’s Common Sense does so, as it allows that human beings cannot help but introduce their own history, experience, and skill into any observation.

Reid found fault with the empiricist’s and the scientist’s separating the senses from the sensors, but he found the rationalist project—to understand the world only through the mind—absurd. For one thing, to pretend that human beings do not relate to the outside world through their senses is silly. For another, although the rationalistic impulse is attracted to a self-evident basis for knowledge—that is, knowledge not based on assumptions—no rationalist could create one. Even Descartes (1596-1650), the father of Enlightenment philosophy, relied on Common Sense in his Meditations on First Philosophy, the seminal text of the Enlightenment. While Descartes said he would assume nothing, not even that he existed, Reid argued that Descartes never actually doubted his own existence for a second and could only make the philosophical claim. Furthermore, Descartes’ famous conclusion, “I think, therefore I am,” does not prove that an object (that is, the thought being had) must have a subject (the thinker having the thought) even though Descartes treated it as self-evident. Consciousness is not logically self-evident, but it is one of the fundamental beliefs of Common Sense. Descartes, according to Reid, just arbitrarily decided that his own consciousness was more compelling than his own existence. If Descartes could not even conduct the mathematically rigorous argument for his own existence without relying on Common Sense, then the entire rationalist project is a charade.

If the impulses of the Enlightenment project are discredited, and if the Enlightenment philosopher is a pitiable thinker overburdening himself with making knowledge indubitable while relying on Common Sense (foundational beliefs and faculties), then what are the solutions to the problems the Copernican Revolution and the Thirty Years’ War posed? If Christians, supposed possessors of divine revelation, are killing each other over unprovable metaphysical issues, how can we tell who is right? If we are not objective but rather subjective observers, how can we come to truth? If the obvious answer (like the sun revolving around the earth) is not always the right one, then how do we know when we have made an error? If our senses can be deceived, how can we trust them?

Reid argued that part of Common Sense is what he called the “principle of credulity”—that is, we can expect others to give us reliable information—and he saw it as essential to solving all of these problems. For example, he argued, everyone who speaks English expects everyone else who speaks English to continue using English words the same way. If we did not possess such a principle of credulity, why would we expect ‘daughter’, for instance, to mean ‘daughter’ and not ‘cow’? We cannot help but assume consistency in the use of English. Furthermore, not only do we assume that the way people speak to us will remain constant, but we expect that the content of what they say will be trustworthy. This is why lying works at all. If human beings were inclined to disbelieve, or to be neutral about, everything a person said, lying could not work. The fact that we rely on other people to tell us the truth is the very reason we are vulnerable to lies. Finally, Reid argued, just as we are inclined to expect English words to have a consistent meaning, we also expect Nature’s language to remain consistent. If English is a means by which we use verbal signs to communicate that which is in our minds to another English speaker, so smell, taste, sound, touch, and sight are the means by which Nature gives us signs about itself. We are inclined to believe our senses, just as we are inclined to believe English words will have the same meaning. And just as we have the capacity to figure out when we are miscommunicating in English, so we possess the capacity to figure out when our senses are not interpreting Nature correctly.

The problems facing the Enlightenment, then, find their solutions, for the most part, in Reid’s principle of credulity. The principle leads us to understand that it is not unreasonable to believe others’ words without the proof demanded by the empiricist impulse. Therefore, unless other factors warn us that the source is unreliable, it is perfectly acceptable to believe someone’s account—for example, Jesus’ account of God’s interaction with humanity and the apostles’ accounts of Jesus’ teaching and miracles.

Just as the principle of credulity leads us to believe others will convey reliable information, Reid implies another principle as well: that all human beings share the same Common Sense. How else could we expect to interact with each other? The scientific impulse wishes to objectify everything, which is not necessary if Common Sense is common to all. Subjective information influencing a conclusion (rather than its being based only on the objective data the scientific impulse demands) does not make a conclusion unreasonable—that is, if the conclusion is consistent with our shared Common Sense. Polanyi wrote that if we could find the coordinates of every atom in the universe, this information would be completely useless because, despite being a comprehensive collection of all observable data, it is irrelevant to anything of interest to human beings. In other words, the most objective catalogue of data must be put into terms that make it relevant to human beings. Reid would heartily agree.

Having shown how Reid would respond to the empiricist and scientific impulses, how then would he respond to the rationalistic? How would he solve the problem of the obvious answer not always being correct? Again, he would look to Common Sense: any conclusion must be consistent with all the principles of Common Sense. Clearly, in the case of the sun going around the earth, the information we gather from our senses inclines us toward a certain solution. Yet, other faculties find the heliocentric model more attractive. What these faculties are exactly is hard to say, but the error of the rationalistic impulse is to believe that just one faculty (in this case, the sense of sight) overrules all the others. Human beings are complex, and we assess and make judgments about complex issues in ways that are not always articulable.

Many in our day have imbibed the empiricist, scientific, and rationalistic impulses of the Enlightenment. Like David Hume, they believe that any valid argument must not take into account anything unobservable; in the extreme, arguing that values like love and justice do not exist, for where are the love and justice molecules? Or perhaps they will only accept scientific studies or beg that everything be quantified. Or perhaps they pretend they are stuck in the Matrix and that there is no external world. Even so, these imbibers cannot help but rely on the foundational beliefs and intrinsic faculties that Thomas Reid labeled Common Sense. Despite their philosophy, these children of the Enlightenment act like selves, do not step in front of buses, and believe that English is a viable means of communication. If Common Sense could free philosophy from the tyranny of Enlightenment impulses, could we not only know but also share the secrets of life, death, and God?