A Response to the Scandal of Disagreement
Dr. Robert Augros
Professor of Philosophy
Magdalen College of Liberal Arts
St. Vincent de Paul Lecture and Concert Series
Thomas Aquinas College, New England
January 17, 2020
[Preface: I should like to thank all the students and faculty who participated in the Q & A after my talk. Your questions and contributions have allowed me to sharpen and clarify many points. By the way, doesn’t this also illustrate how opposition can advance the truth? In some of the footnotes below, I have summarized the main points that I remember from the discussion, introducing them with the marker “Q & A”.]
I would like to dedicate my remarks this evening to the memory of Dr. Duane Berquist, a great philosopher and teacher, well known to Thomas Aquinas College. He has been my guide and mentor for my entire adult life and were it not for his rich teachings, which originally attracted me to philosophy, I would not be standing here before you tonight.
Now Thomas Aquinas College is well-known for centering its curriculum on the Great Books of the Western World. But one of the first things a student notices about these books is that many of them say opposite things. This poses a problem for how the beginner can learn from them and also raises the larger question of whether we can learn anything from philosophers, if they cannot agree among themselves.
Imagine if carpenters could never agree on anything. If you ask one, he insists plywood is the only sensible choice for your project. If you ask another, he says, above all, you should use anything but plywood. Every book published on carpentry is quickly followed by another book that attacks all the principles and conclusions of the first. No two carpenters can agree on how to build a deck, a chair, a wall, or a house; nor on what tool to use for any procedure, or even on what carpentry is. Would this not provoke anyone to despair and justify concluding that there is no such thing as the art of carpentry?
Philosophy seems to be in this very predicament. From its inception it has been plagued by disagreement. Some philosophers have said there is only one elementary substance, others that elementary substances are infinite in number and in kind. Others deny that any substance can be known. Some philosophers say all human knowledge is derived from sense experience; others, that intellectual knowledge does not at all depend on the senses; and still others, that there is no human knowledge. Some say happiness is pleasure; others, wealth; others, honor; still others, that the highest good is different for every individual. Philosophers say contrary things both about the starting points and about how to proceed in philosophy. They even disagree on what philosophy is. David Hume writes, “There is nothing which is not the subject of debate, and in which men of learning are not of contrary opinions. The most trivial question escapes not our controversy, and in the most momentous we are not able to give any certain decision. Disputes are multiplied, as if everything was uncertain.”  No subject is free from these conflicting opinions. It seems every philosopher has a philosophy all his own. This universal disagreement appears to discredit philosophy completely and is a perennial scandal.
What is the most reasonable thing to do when authorities disagree on an important question? Historically, there have been three different reactions. The first is typified by Michel de Montaigne, a 16th-century essayist, for whom the many opposing views of philosophers is itself sufficient proof that no resolutions are possible. For Montaigne philosophy consists in merely listing the opinions and then moving on to the next topic, without ever attempting to resolve the question. This kind of radical skepticism actually dominates academia today. Philosophy can be no more than the history of what philosophers have thought and said, we are told. Instead of “Let no one ignorant of geometry enter here”, the sign above the entrance to the modern academy says, “Abandon all hope of the truth ye who enter here.” Anyone who dares to say he has found some “truth” outside of science, is scorned and ridiculed. Believing that there is such a thing as truth is taken as proof of arrogance.
What should we make of this utter skepticism which is the expression of a profound intellectual despair? First of all, we should point out the self-contradictory nature of radical skepticism. If someone says, “No truth can be known,” then he is asserting something he thinks is true and that can be known. Every denial of the possibility of truth, assumes truth exists. Thus, there is no need to argue against radical skepticism. It self-destructs. It is absurd to use reason to attack reason. The skeptic is sawing off the limb he is sitting on.
But we can say more. Montaigne and modern thinkers are counseling that we give up the enterprise. Is philosophy that impossible? If something is difficult, there are always those who will call it impossible. For decades field and track commentators proclaimed that it is physiologically impossible for a human being to run a mile is less than four minutes—until May 6, 1964 when Roger Bannister ran a mile in 3 minutes and 59.4 seconds, a record that lasted only 46 days. The four-minute barrier has since been broken by over 1000 male athletes, some of whom were in high school at the time. In our criminal justice system, disagreement does not cripple a trial. The prosecution and the defense each present the strongest case they possibly can, but we do not conclude that no verdict can be reached because of the opposing views. In science also, contradiction does not produce despair. In the 19th and 20th centuries when physicists found strong experimental evidence that light is a particle and that light is a wave, they did not despair, but worked for a resolution, which ultimately led to the development of quantum theory.
Also, the skeptics may be making more of a statement about their own personal incapacity than about the impossibility of finding solutions. Perhaps Montaigne, when he throws up his hands, is telling us more about his own inability than about philosophy. There is, after all, the eight-year-old boy who declared, “No one can lift 100 pounds. I know. I tried it.”
But the most telling rejoinder to the skeptic comes from nature herself. Every man has a natural desire to know and natural desires are not in vain. For example, every animal has a natural desire for food. This does not mean no animal ever starves, but it does mean that the food for each species exists in nature and is, in principle, possible to attain. Likewise, man’s natural desire to know does not mean everyone attains the truth, but that truth exists and is possible to reach with the equipment nature has given us, senses and a mind. Even the skeptic gives witness to the natural desire to know because he has despaired, and no one despairs over something he never desired in the first place. One thinks of the Aesop’s fable with the fox and the “sour” grapes. There is something too facile and cowardly in this first reaction. It is unworthy of a wise man.
Rene Descartes, the father of modern philosophy, read Montaigne and was dissatisfied with his skepticism. In response to disagreement, Descartes offers a different proposal. He explains that he experienced bad teachers in college and concluded that none of the persons who taught him really knew anything. And since previous philosophers disagree with each other, he concluded none of them had the truth either, because if one did, he would have convinced the others: “There is in the sciences scarce any question about which men of ability have not disagreed. Now whenever two such men are carried to opposite conclusions regarding one and the same matter, one at least must be in error; indeed, neither of them, it would seem has the required knowledge. For if the reasoning of either of them were certain and evident, he would be in a position to propound it to the other in such wise as to convince him also of its truth.”
So, Descartes decides to reject his predecessors and contemporaries and begin philosophy again by himself. If you want something done right, do it yourself.
Now this proposal is an improvement over Montaigne. Descartes has hope that we can attain truth and satisfy our natural desire to know. But, Descartes’ reaction has shortcomings of its own.
To accomplish difficult things, we need all the help we can get. In waging a war, for example, we need as many allies as possible. So Descartes seems to be assuming that finding the truth in philosophy is easy. It is so easy you can do it without anyone’s help. A sign that this is false is the disagreement that Descartes admits. People do not disagree on easy and obvious things, like what the square root of nine is.
Also, there are some areas of knowledge where Descartes’ proposal is impossible. To learn a language, for example, we necessarily depend on other persons who already speak that language. Did Descartes make all of his own clothing, grow his own food, heal himself when sick, and manufacture all the items he used? Human beings naturally depend on others in many ways. It is natural to do so in the intellectual life also. Venerable Bede once wrote: “As no one receives existence from himself, so no one can from himself be wise.” In my opinion the four wisest men is human history were Plato, Aristotle, St. Augustine, and St. Thomas Aquinas. NONE of these men tried to achieve wisdom all alone. Plato spent ten years as a disciple of Socrates. Aristotle spent 20 years studying under Plato. St. Augustine had St. Ambrose and St. Thomas was formed by St. Albert the Great.
Furthermore, why not use the insights of those who have gone before us? If ten men sincerely try to solve a problem, even if they all fail, one or more is bound to stumble upon some useful insight. To reject them is to throw all this away. Even if they fall into grave errors, we can still learn from them not to make the same mistakes. But we cannot do this if we reject their views wholesale. If one man investigates without the help of others, he is more likely to discover only a part of the truth rather than the whole of the truth. But why not gather the parts? If you refuse to, you run the risk of never knowing the whole truth about anything. We may also ask, what is Descartes assuming about his own mental ability? He seems to be saying, “Where all these other great minds have failed, I will succeed with help from no one.” This is a far cry from the humility that characterized Pythagoras and the ancient philosophers.
Moreover, Descartes cannot avoid inconsistency. If we follow his example by rejecting our predecessors, we will reject all of his ideas and begin anew ourselves. So he leaves a self-defeating heritage. Philosopher Thomas Hobbes wrote elaborate objections to Descartes’ Meditations. Descartes subsequently published all of Hobbes’ objections along with his own rebuttals in the next edition of the Meditations. Hobbes’, however, still persisted in his criticisms. This so angered Descartes that, after several exchanges, he refused to have anything further to do with “that Englishman”. But since Descartes failed to convince Hobbes, we must conclude, by Descartes’ own principle, that he did not possess the truth. Thus, Descartes refutes himself.
Philosophers after Descartes disagreed with him on most of the important matters. By his own standard, then, he would have to admit he did not know what he was talking about. Disagreement was the problem Descartes began with. But then he is discredited because he disagrees with himself. Descartes is not at all solving the problem of disagreement; he is making it worse. His position will be just adding one more opinion to the collection of conflicting opinions that already exists, with nothing to distinguish itself from the rest.
A third response to disagreement is found in thinkers like Aristotle, St. Thomas and many others. It counsels this: When faced with disagreement, begin again, but with the help of your predecessors. This alternative avoids the contradictions and other defects of the first two reactions. Any opinion that somehow incorporates the parts of the truth in previous views is qualitatively different from them all. Surely this is the most reasonable approach, but exactly how can it be accomplished? Let me illustrate using the two previous approaches to disagreement we have just discussed.
Montaigne and Descartes represent two extremes; Montaigne says wisdom is impossible; Descartes says it is so easy, you don’t even need help to attain it. As they stand, these two positions are utterly incompatible. Though each has some part of the truth, neither side can acknowledge the truth that the other side has seen. Descartes will never admit philosophy is impossible and Montaigne will never agree that it is easy.
Let us see if we can’t reconcile these two irreconcilable opinions. We can begin with a very general principle: The more contains the less. For example, if Achilles can lift 200 pounds, then even more so, he can lift 100 pounds. The more contains the less.
In the same way, anyone who say something is easy must also say that it is at least possible. And anyone who says something is impossible must also say that it is at least difficult. Now possible and difficult are not opposites. In fact, they are quite compatible. It is difficult but possible to run a mile is less than four minutes; difficult but possible to pass the bar exam. The common ground between impossible and easy is to say finding the truth amid disagreement is difficult but possible. This puts us in a position to see the part of the truth in what each man is saying. The middle position is more probable than either extreme and has none of their defects or self-contradictions. This resolution of opposites is like a sieve that filters out the dross and preserves only the gold. Behold the disagreement resolved! And here’s the important part: we did it with the help of our predecessors, Montaigne and Descartes.
We can draw a further valuable lesson from this disagreement. Plato and Aristotle teach that the catalyst for philosophy is wonder, an emotion compounded of three elements: the desire to know, the fear of error, and the hope of overcoming the obstacles that stand in the way of the truth. If any of these components gets out of balance, wonder is destroyed and the whole intellectual life is compromised. If there is too much fear, it paralyzes the mind and produces the despair of skepticism, as with Montaigne. Overconfidence, on the other hand, causes the rashness we see in Descartes. Again, their conflicting opinions have been extremely instructive.
Philosophers agree much more than is realized. The agreement is seldom on the surface, however. For example, the first Greek philosophers disagreed radically on what the principles of nature are. Please direct your attention to the chart on a separate page which divides out their opposing opinions.
Quite a smorgasbord of opinions. Nine possibilities and a thinker in every slot. Every opinion here is contradicted by eight other opinions. What could be more hopeless? Yet Aristotle says something very shocking about these opinions. In effect he says, all these men are saying the same thing. What??? How can you say that when their claims all contradict each other? It would be difficult to invent a more divergent set of opinions.
Nevertheless, Aristotle sagely points out that Thales explains change by expansion and contraction of water. Empedocles accounts for change by assembly and disassembly of his four elements. The atomists, Democritus and Anaxagoras, use congregation and separation to explain change. “Even Parmenides”, Aristotle remarks, “treats hot and cold as principles under the names of fire and earth.”
What do all these pairs have in common? They are all opposites. Aristotle is right. All of these men take it for granted that change is between opposites. This hidden agreement is astonishing! The surface discord hides a deeper harmony that provokes wonder. These philosophers seem to have a secret pact that even they themselves are not fully aware of. And it is especially encouraging because whatever they all agree on is more probable than what only one of them says. Aristotle then verifies this insight with an induction, looking at the various kinds of change. Then he confirms it further with reason, showing if there is no opposition, no change is possible. If something goes from being white at 10 A.M. to being sweet at 11:00 A.M., there is no guarantee of a change, because white and sweet are not opposed. Sugar is both. So, the disagreement of the First Philosophers leads us, with the help of Aristotle, to discover the first and most evident principle of changing things: change occurs only between opposites. By the way, Aristotle draws not just this insight from the first philosophers but many others as well. This is the very finest use one can make of one’s predecessors. Many winters ago, when I was an undergraduate just beginning in philosophy, merely seeing this would have been sufficient to make me a disciple of Aristotle for the rest of my life.
We must not allow the surface disagreements among philosophers to make us overlook any hidden agreements they might have. By the way, this is a good illustration of tradition at its very best. Tradition is not mindlessly repeating the past. Tradition is advancing a science or an art by building on what is best in your predecessors and using their help.
Sometimes what thinkers agree on is true and insightful but at other times, they agree on a common error. Take the current conflict between the evolutionists and the creationists. One side says natural selection produced all species of animals and plants so there is no need for God. The other side insists that because God created all animals and plants, evolution is a hoax. Despite their opposition, both sides agree on an unspoken premise. Both assume that if one agent is responsible for the entirety of an effect, then another agent cannot also be responsible for the entirety of that same effect. You can paint part of this wall green and I can paint the rest. But if you paint the entire wall green, I cannot also be the agent cause of the same effect at the same time. In such cases a second agent is superfluous.
This tacit premise certainly seems true, even obvious. But it is false. I and my paint brush are both at the same time agent causes of this entire wall being painted green. There is no impossibility as long as one of the agents gives the other one its causation. I move and direct the paint brush to paint the wall. It is an instrumental agent while I am the principal agent. We can even add a third agent. My foreman directs me to paint the entire wall green.
If you remove this error the disagreement vanishes! There is no impossibility in both God and evolution being agent causes of all animal and plant species, provided God uses evolution as a tool. This is an especially satisfying resolution because it enables us to agree completely with the positive premises on both sides.
We notice a pattern here. Not only is there often surprising agreement below the surface, but that agreement or some other common ground offers a key to resolving the question. Let’s test this with more examples.
One of the most extreme clashes of opinion in the history of philosophy occurred between Heraclitus and Parmenides. Heraclitus insists that all things are constantly changing, while Parmenides contends that nothing changes because change is impossible. How could there be any common ground between these two opinions? A careful reading of their views reveals that they both agree that change entails a contradiction. They say this because change is between opposites, but how can hot itself become cold without a contradiction? Agreeing that change entails a contradiction, they then go their separate ways. Heraclitus argues that change is evident to the senses and therefore change exists. And if it entails a contradiction, so be it. Parmenides asserts that contradictions are impossible and therefore change is impossible, and we must not trust our senses in this matter. Their conflicting conclusions, that everything is changing and that nothing changes, point to the premise they agree on: change incorporates a contradiction. This is the questionable assertion in their reasoning and if we can show it to be false, we shall not only learn something important about change, but we will have resolved the opposition between Heraclitus and Parmenides. We can then agree with Heraclitus that motion exists and with Parmenides that contradictory things are impossible. The common ground underlying their disagreement told us where to look. 
Here’s another case. In 1914, the southern United States was blighted by pellagra. Two expert research teams composed of famous doctors could not find a solution, but surmised that pellagra was a contagious disease caused by an unknown microorganism, a bacterium, probably spread by the stable fly. Then the Surgeon General of the United States sent Dr. Joseph Goldberger, an experienced epidemiologist, to take a fresh look at the case. After pains-taking study, Dr. Goldberger concluded that pellagra was not a contagious disease at all but resulted from a dietary deficiency. The southern experts scoffed at Goldberger and tried to discredit him. A hopeless impasse that calls for despair? Not at all. If we look for what both sides agreed on, we shall find the key to resolving the dispute. Both sides agreed that the matter should be settled by a scrupulous application of the scientific method. The southern team pointed to the great success of Louis Pasteur and others in explaining diseases by isolating their bacterial agents. Pellagra was likely to be a similar case. Dr. Goldberger, while not denying any of this, devised multiple, meticulous experiments and control groups that conclusively proved pellagra was not contagious but was caused by lack of sufficient niacin in the diet. Both sides accepted the scientific method as authoritative in this question and it finally led to the truth, despite the southerners who continued to reject it, even after the evidence was in. Behind many philosophic disagreements there lies a deeper, more significant agreement that incorporates the resolution to the problem.
There is another important kind of hidden agreement. We may call it unconscious and involuntary. Suppose someone denies freewill. After we have shown that his arguments against it are no good, we can take the refutation one step further. We can point out in what the opponent says or does something that shows he himself also believes in freewill, despite his protests to the contrary. In his unguarded moments. he will praise or blame someone, or say what he is planning to do this afternoon. Neither of these makes sense unless we are free. This means if we look beyond what the determinist says with his mouth and pay attention to how he lives, he, too, will give witness to freewill. It is a strong confirmation of freewill that even those who try to deny it cannot avoid assuming it.
It is the same for anyone who denies any self-evident truth. Some philosophers have denied and ridiculed universal ideas. Not only can we show their arguments are fallacious in this regard, we can easily catch them thinking and reasoning with universal ideas. This is because they think with human minds just like our own and everyone else’s.
So far, we have examined several cases of disagreement and shown how they can be resolved. Now we are in a position to make a much stronger statement. Not only can conflicting opinions be resolved, they are a necessary step in searching for the truth. In fact, the absence of disagreement can prove a hazard. If we encounter a statement that happens to be false, we are more likely to be taken in by it if there is no opposition to it. For example, the poet Baudelaire claims that the imagination is the “queen of the faculties” and makes a persuasive case for it. Blaise Pascal, however, calls the imagination “the mistress of error.” Without this opposing view, we might adopt Baudelaire’s assertion uncritically. The most productive thing you can do with an extreme opinion is to put it up against its opposite. That will always tame it somewhat. Similarly, we might be taken in by Descartes’ declaration that motion is so easy and obvious that it does not even need a definition, were it not for Zeno’s serious objections against the very existence of motion.
Opposition fosters the element of caution in wonder and prevents us from rashly grabbing at the truth. Opposing opinions also help to prevent us from overstating our case, and are likely to expose any ambiguity in our premises and assumptions. We see this principle applied in politics. One function of the loyal opposition party that is out of power, is to keep honest the party that is in power. Analyzing conflicting opinions before trying to judge a difficult matter is like listening to the advice of many people before making a difficult decision. There is a much better chance of taking all important aspects into account. Not being exposed to disagreement on a topic is like someone raised in a germ-free atmosphere. His immune system has not developed and he will fall victim to the first bacteria he encounters when he leaves his sterile environment. Similarly, by considering opposing points of view we develop an immunity to weak arguments.
Aristotle, in all of his treatises, before trying to settle a matter definitively, develops the opinions of his predecessors, using dialectic to argue to opposite conclusions. He explains the need for this procedure:
“To doubt well …is necessary for those wishing to discover. For the discovery afterwards is an untying of the difficulties before…those investigating without having first considered the difficulties are like those who do not know where they ought to go; and, in addition, do not know if the thing sought has been found or not.” Someone who does not see the difficulties does not know how to proceed and will not recognize a solution even if he happens to stumble onto it by chance.
Opposite opinions not only help us discover the truth but can also confirm it, after it is discovered. In the Nichomachean Ethics, Aristotle begins the discussion of happiness by carefully consulting his predecessors on the subject. Then he rigorously reasons out the definition of happiness. Then, in the next chapter, he takes the trouble to show how his own answer takes into account all the parts of the truth found in the views of others, saying, “With a true view all data harmonize, but with a false one the facts soon clash.” For he maintains it is not probable that their opinions are entirely mistaken, “but rather that they should be right in at least some one respect or even in most respects.” In this way, we learn that Aristotle’s conclusion is more probable than any of the others, since it unites in a single definition all the parts of the truth found separately in theirs, without any of their defects. Thus, he has used conflicting opinions in a wonderful way to confirm the truth.
But what happens if no one before you has addressed the topic you wish to investigate? Aristotle was the first to write a treatise on metaphysics. Thus, he had no conflicting opinions of predecessors to work with. So, what does he do? He himself constructs opposing arguments on all the most important questions in this new science! He devotes the entirety of Book III of the Metaphysics to this, before trying to resolve the questions definitively.
Conflicting opinions are to the wise man what lumber is to the carpenter. Without lumber, a carpenter cannot proceed to make anything. Likewise, without disputes and disagreements, a wise man cannot resolve difficult matters.
This is also true in science and theology. A colleague of the great physicist Niels Bohr remarked, “Difficulties were for him merely the external appearance of new knowledge, and in an apparently hopeless contradiction, he conceived the germ of wider and more comprehensive order and harmony.” We already mentioned that in the 19th and 20th century, physicists found evidence that light is a particle and evidence that light is a wave. Out of this conflict eventually came the new insights of Quantum mechanics. Einstein says about his own theory, “Relativity theory arose from necessity, from serious and deep contradiction in the old theory from which there seems no escape.”
In theology we find the same role of disagreement. Theology was born with the Fathers of the Church working to resolve apparent contradictions between different passages of Sacred Scripture. Reconciling these seeming contradictions led to a deeper understanding of the faith. We notice in the Summa Theologica, every article begins by giving the reader several reasons for disagreeing with what St. Thomas is about to say. Then, after giving definitive reasons for his own teaching, he shows how it enables us to answer the arguments to the contrary.
Hence, disagreements are not an embarrassment or an occupational hazard in the life of the mind. They are an essential part of the enterprise. To discover and confirm the truth, the philosopher, the scientist, and the theologian must seek out and actively cultivate difficulties and disagreements.
The resolution of any disagreement requires finding a deeper level of agreement, some kind of common ground between the disputants. In some cases, this will be a common premise, true or false, that both sides agree on. In other cases, we can reduce both sides to a more probable middle position. If neither of these options is available, we can still have recourse to some neutral, reasonable procedure to settle the matter. Even where opponents do not agree on a conclusion, they can often agree on the method to settle their differences. For example, let’s say you and I disagree on how many square feet of floor space there are in a certain room. You say it’s 450 and I say 600. We do not agree on the conclusion but we do agree on a valid and rigorous way to decide who is right: measure the length and width of the room and multiply the two numbers.
In legal matters, two litigants who disagree about who owes who money can settle their dispute if they agree to submit themselves to the authority of the law. The unbiased procedures of the court are common ground.
Recourse to a common method can resolve conflicts of opinion in science. If two physicists have contrary hypothesis that explain the same phenomenon, they can resolve their disagreement by devising an experiment that will lead to different results for each hypothesis.
In philosophical disagreements we can always fall back on the common ground of statements that are self-evident to everyone and the laws of valid reasoning common to all human minds. No disagreement can be resolved without having recourse to some kind of common ground. Many centuries ago, Heraclitus said, “Those who speak with understanding must be strong in what is common to all.”
In conclusion, we have seen that disagreement is a potential obstacle to truth, but that is not the whole picture. Disagreement is also a necessary means to the truth. Even when one side is entirely correct, its truth will become more evident when we see its power to dismantle the apparent evidence supporting the opposite side. The wise Roman stoic, Epictetus, once said, “The beginning of philosophy is the recognition of disagreement. Then it seeks the cause of it. And then discovers some principle to distinguish what seems to be true from what is really true.”
That philosophers disagree is obvious. Nobody misses that. What many people do miss, however, is the underlying common ground and the many discoveries that a study of the conflicting opinions can bring to light. The philosopher does not give up in despair when there are opposing arguments on a given subject. Instead he seeks a solution. The skeptics say that philosophy ends with disagreement. Wise men say it begins there. For the philosopher, then, disagreement is not a scandal… but an opportunity.
 Treatise on Human Nature, p.3
 Q & A: One student asked for a proof that proofs are possible. Attempting that would be circular and futile. It doesn’t work that way. What’s the best way to prove that a human being can run a mile in less than four minutes? Not a priori arguments from anatomy and physiology. Just have someone do it. “Ab esse ad posse valet illatio” said the scholastics, the inference from being to possibility is valid. In this way the ancients Greeks did not try to prove that proofs are possible. They first proved some particular thing to everyone’s satisfaction. Then they said, “Hey, we really proved that the base angles of an isosceles triangle are equal! Always and necessarily. Now, how the heck did we do that??”. We first find proofs of things and then, by reflection, realize that proofs are possible and subsequently discern the general tools for proving things. Modern philosophers err when they begin with the question, “Can we know anything?”. Every question presupposes we known some things already. You have to have some awareness of what knowledge is and what it means to say something is possible before you can ask “Can we know anything?” The first question is not “Can we know?” but what do we know and the second is how do we know. Socrates spent his life on the first of these. Plato and Aristotle explored the second, developing dialectic and logic.
 The desire for agreement is not entirely misguided. It is natural for the mind to want to see how all things harmonize, even opposing opinions. We might compare it to a desire for world peace. But it is unrealistic to expect that everyone will agree even when the truth has been thoroughly and definitively proven. The purpose of philosophy is not to force people into agreement. It is to understand the truth.
 Rene Descartes, Rules for the Guidance of Our Native Powers; Rule II, p. 5.
Q & A: This is the ultimate reason why Descartes rejects his predecessors. Please notice that Montaigne would agree whole-heartedly with this principle. Another hidden agreement! But this principle is false. If it were true, we’d have to say that Galileo could not have known that Jupiter had satellites, since many natural scientists of his time thought the idea was preposterous and even refused to look through his telescope. Or, despite many successful experiments and control groups, Louis Pasteur could not have known that vaccination prevents anthrax in animals, since his scientific colleagues ridiculed the idea at the time. Therefore, the reason why Montaigne and Descartes reject their predecessors is unsound and unreasonable. We notice in this principle that Descartes concedes too much to skepticism.
A further point. If something has been genuinely demonstrated, is dissent always based on ignorance and prejudice? Even unbiased, intelligent persons can be deceived by a strong, misleading appearance. Something true can lead us into error, if it masks some more important truth that is difficult to see. A false $20 bill can deceive us, not because it is counterfeit but because it looks so much like the real thing. Why for so many centuries did everyone think the sun revolves around the earth? Because this certainly seems to be true to the casual observer. There is immediately available to everyone a strong, misleading appearance. In the same way, people are deceived by the obvious disagreement among philosophers, which masks their more profound hidden agreements.
 Sunday Sermons of the Church Fathers, p. 144.
 Someone might object that Descartes explicitly says he intends his method for himself alone. But what can such a claim be except rhetoric and false modesty? After all, he publishes his principles in a book entitled Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences. He’s talking about everyone’s reason, not just his own. Further, he claims to have found a universal method applicable to all the sciences. Clearly, he thinks his method is big world news and not just autobiography.
 Q & A: Even universal agreement does not guarantee that we have the truth. Bishop Fulton Sheen once said, “If something is true, it’s true, even if no one believes it. And if something is false, it’s false, even if everyone believes it.” The example we gave is the belief that the sun travels around the earth each day. For more than a thousand years everyone believed this, astronomers and lay people alike. We decided that agreement is not a cause of truth but at most a sign of it. And we should add it is a fallible sign, as the example just cited shows. (For the distinction between fallible and infallible signs, see Prior Analytics II ch. 27.) The most that agreement can produce is probability, not truth. If all economists agree that tariffs are harmful even for the country imposing them, that does not make it true, but it does make it probable. As long as you speak in terms of agreement and disagreement, you are in the realm of dialectic, with greater or less degrees of probability, not certainty. One of the uses of dialectic, the kind of debating found in Platonic dialogues, is to investigate both sides of questions in the sciences and also to discover the principles of the sciences. (See Topics I, 2)
 Q & A: A student objected that Montaigne would never admit this because what is impossible is an absolute and admits of no degrees. Another student very helpfully distinguished two meanings of the word “impossible”. The strictest meaning is something that is intrinsically self-contradictory, like saying seven is both an odd number and an even number. Another sense of the word is something that is not self-contradictory but is absurdly out of the question and will in fact never happen, say Donald Trump being elected king of France tomorrow. Montaigne is probably not saying that finding the truth is self-contradictory but that it so difficult as to be impossible in practice.
 Q & A: Does resolving a disagreement require that all parties end up agreeing? No. We should not expect the resolution of every disagreement to end with singing Kumbaya and hugs all around. Truth depends on evidence, not on counting heads. Otherwise, no court of law could convict a murderer, no matter how overwhelming and clear the evidence against him. All he would have to do is disagree with the verdict and it would automatically become unknowable because disputed. The most stubborn person in the room is not granted arbitrary veto power over a validly demonstrated conclusion.
 Physics I, ch. 5, 188a 18
 Q & A: Dr. Kaiser’s opening question was “If the hidden agreement between disputing parties is sometimes true and sometimes false, then how does it help us resolve the disagreement?” The final resolution of a problem must eventually get beyond opinions and find the truth in things. The only utility of finding hidden agreement is that it helps us toward an eventual rigorous and definitive judgment about things. Aristotle gets a clue from the first philosophers about opposites but then forms an induction from the different species of change to confirm their insight and finally shows how opposites are necessarily in the definition of change.
Thus, in the present example, distinguishing different kinds of agent causes alone does not prove that both God and evolution produced all species, but shows that such a thing is a possibility and that the two sides are not really disagreeing. This does not settle the matter with certainty, much more work must be done, but it has broken the stalemate and pointed us in the right direction.
 To resolve this conflict definitively, we would first need to show that their reason for saying change entails a contradiction is defective. All the first philosophers not only used opposites but also asserted a third thing in change which is not an opposite. Thales says it’s water, Heraclitus, fire; Democritus and Anaxagoras, atoms; etc. To say heat becomes coldness is contradictory, but there is no contradiction in saying water changes from hot to cold. This, of course, is all in Aristotle (Physics I, ch. 7).
 “Bene dubitare” or doubting well implies not merely recognizing conflicting opinions but developing persuasive reasons for both sides.
Q & A: We argued that the universal doubt of Descartes is not a principle either in science or in philosophy. It is unreasonable to doubt everything indiscriminately. We should doubt only those things we have good reason to doubt. Those are the only kinds of doubts that advance the discussion. Imagine someone presenting an impeccable proof for the Pythagorean theorem and someone objects, “But how do we know we are not all insane?”. Such a “doubt” is not pertinent to the question at hand. If the objector pointed out in the proof that two lines were assumed to be equal with no evidence, he would be saying something helpful.
We also distinguished doubt from ignorance and error. Ignorance is having no opinion on a topic either pro or con. You just have never considered the issue. Error is having a definite but false opinion on a subject. Doubt is the indeterminacy of the mind that does not yet know enough about the subject to settle the matter conclusively or even with strong probability. We noted that the slave boy in the Meno passes through all these states and finally reaches knowledge about doubling the square, guided throughout by the careful and orderly questions of Socrates.
 Metaphysics, III, ch. 1, 995a 27 seq.
 Disagreement is a clash between opinions; contradiction is the apparent clash between facts. Scrutiny of both is fruitful and productive.
 p. 234, Niels Bohr, Ed. S. Rozental, Wiley & Sons, N.Y.
 p. 192.
Q & A: One student raised the difficulty that if each new scientific theory replaces the old one completely, then how can we ever be sure of knowing the truth about anything, since it might be replaced in a few years. This is a concern only if the new theory annihilates the previous one. The history of science shows otherwise. Every new paradigm has to incorporate all that is true and well established in the old, while fine tuning other parts and adding new insights. For example, relativity theory retains Newton’s laws for every-day objects and makes adjustments only in special circumstances. This is the natural progress of human knowledge. (This understanding of progress in science connects with our remarks on tradition on page 9.) If on campus I identify an organism as a tree, that is real knowledge, though vague and incomplete. If I later identify it as an eastern white pine, that adds to my knowledge of it without destroying what came before. It is still a tree. Dr. Kaiser pointed out that Foucault pendulum demonstrations prove definitively that the earth rotates. [See internet for explanation.]
 Do we have to assume that all disagreements can be resolved? No. There are cases where there are probable reasons on both sides but insufficient evidence to settle the issue once and for all. Aristotle gives the question “Whether the universe is eternal or not” as an example (Topics I: 11). We cannot prove or disprove the existence of extinct animals that left no fossils or other traces. The only thing I insist on is that not all cases of disagreement are impossible to resolve. If they were, then philosophy would be pointless. We have given several examples where disagreement actually helps us to resolve the dispute and discover the truth. Beginners in philosophy do not have to be able to resolve all disagreements. They just need encouragement that such resolutions are possible. This gives them hope, takes the sting out of disagreement, and removes the scandal, which was the goal of my talk.
 Common ground is not necessarily middle ground. If one man says all right angles are equal and another says none are equal, the truth does not lie in the middle: some are equal and some are not.
 Self-evident principles are found not just in geometry but in every science and art. In natural science there is “Nothing comes from nothing”; in ethics, “The end is more desirable than the means”.
 Q & A: But what if somebody denies the common ground, claiming he has his own logic and his own truth? You are allowed to have your own opinion but not your own facts. A man who refuses to accept anything common can no longer disagree with anyone! What if someone says, “I choose to reject the laws of physics and the legitimacy of experiment”? Then he has also chosen to take himself out of any scientific conversation. Do you reject ordinary language? Then you cannot communicate with anyone. What is more, you will not be able to express your own opinions even to yourself. You have rejected the life of the mind and embraced the vegetative life. You can deny anything you please, but some denials incur consequences and penalties.
 DK 114.
Q & A: Every disagreement is built on agreement. The disputing parties must agree on the subject they are discussing. If you tell me all right angles and are equal and I say, “No, no,no! All frogs are amphibians”, we are not disagreeing. And the two parties have to be saying incompatible things about the same subject. If you tell me all horses have four legs and I protest that all horses are mammals, we are not disagreeing. Both statements are true. There can be pseudo-disagreements, as seen in the creationist-evolutionist example above.
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