The Sources of Knowledge


All of us have stored away millions of bits of information, most of which, as we all know, we can’t remember when we want to. What is the source of these bits of information? How we get them into our mind and into our memory?

Most of us realize that many of those bits of information we have stored away are erroneous, false, or just plain ridiculous. Part of our task in living is to separate the true from the false, the correct from the incorrect, the real from the unreal, the dream from the reality, the sensible from the foolish, and so on.

Furthermore, we are bombarded day in and day out with information. This information comes from many sources and is either reliable or not reliable. How do we distinguish the reliable information from that which is not reliable?

Almost everything we know originates from the sources of knowledge to be described below. Our primary source of information is our own senses, the capacity we have to see, hear, touch, smell, and taste. There are other sources we may call secondary, such as reason, intuition, and authority. Finally, there are sources we may call problematic. These latter sources, including things like extrasensory perception, anamnesis, racial memory, the occult, and supernatural revelation, are questionable or controversial or lack any final and conclusive resolution.

Let’s take a brief look at the main sources of knowledge from which we have obtained virtually all of our information. We’ll suppose that we are gathering “evidence” for our arguments and theses sources are what we are appealing to as grounds to support our propositions.

The Appeal to Sense Perception

We can make an appeal to sense perception. This is the process of relying on the physical senses and concrete experiences for information. Our senses are the basic source of information we have used throughout our life beginning from the time we are born (and possibly before, according to some researchers). We became acquainted with the world around us through the use of our sense organs.

Through the use of our external physical senses, we learned that certain things in our world were sweet while others were sour, certain objects would cause pain while others cause pleasure, that fire is hot and can burn, that certain objects could frighten us, or soothe us, or make us smile. All this information became part of us and built a web of knowledge which we could use to interpret our world, survive in it, and attempt to control it.

We also have internal physical senses which inform us about things going on inside us. We have nerves inside our bodies which give us information about our internal state and also provide us with information about physical coordination, equilibrium, and so on. Generally, we don’t appeal to our internal physical senses for evidence in an argument. No one else can experience our internal sensations, they are strictly private affairs, and are seldom the basis for controversy.

An appeal to our external senses for evidence, however, can be subject to controversy. Are we really “seeing” what we claim to see? Can we be sure that our external senses are reporting to us correctly? Can we believe what our senses seem to tell us?

Some people have argued that we don’t get a “true picture” of the world through our senses. Others have argued that the world is presented to us just as it is. We’ll forgo for the present trying to solve this controversy as it would get us far afield into another branch of philosophy called epistemology. This much can be said at this point. Our senses simply report something to us and we do not get into matters of truth and error or the true and the false until such time as we express a judgment about what we see, hear, feel, smell, or taste. Only judgments and propositions expressing judgments can be true or false.

We need to be aware, however, that some cautions are necessary when we make an appeal to sense perception as grounds for asserting the truth of a proposition. Prejudices and emotions can distort our view so that we select “facts” to support our expectations. We also tend to see many times what we expect to see or are trained to see and our observations can be infected with a personal and subjective coloration.

The Appeal to Common Sense Opinion

Many times in an argument, an appeal to common sense opinion will be made. What do we mean by common sense opinion? We should consider common sense opinion to refer to that fund of opinion each member of a group has, including generally accepted knowledge which has been more or less empirically verified and the ways of thinking and acting passed on from generation to generation by tradition, imitation, and instruction.

We conduct many day to day affairs on the basis of common sense opinion. And this works for most of us most of the time. However, an appeal to evidence derived from common sense opinion is not without its dangers. The appeal can be a means of justifying preconceived beliefs which, if better scrutinized, would not be adequate grounds for accepting the truth of a proposition. Many people believed for a long time that the earth was flat, based on common sense opinion. Some people believe there are races of human beings who are inferior to other races because it’s just common sense opinion.

Common sense opinion may also present other problems. It tends to be habitual and imitative and may discourage obtaining better information. Common sense opinion is largely inherited from the past and may inhibit progress. Often, common sense opinion is vague and ambiguous and a considerable part of it may be untested belief, seldom accompanied by adequate explanations.

All this does not mean there is no value in appealing to common sense opinion. It does mean that just because some proposition appears to be justified by common sense opinion, that proposition, particularly about an important matter, may have to be carefully scrutinized, critically analyzed, and subjected to outside tests of truth.

The appeal to common sense opinion is related to the appeal to “authority.” Most of what we have accepted as common sense opinion has come to us through authorities such as our families, friends, social institutions, and our culture in general.

The Appeal to Authority

We, as individuals, don’t know everything. In fact, we can’t know everything. There is simply too much information out there for us to know it all. We rely on other people to provide us with much of the information we need. When we appeal to authority as a grounds for supporting a proposition, we are accepting someone else’s position or facts and relying on their testimony.

Most of what we learn in school is given to us on the basis of an appeal to authority. It is second-hand information, handed down to us by hopefully reliable authorities. In arguments, we may appeal to authoritative sources to back up some claim we make. We look to medical scientists as authorities on health and disease. Court trials depend on the use of “expert” witnesses who are authorities in their field. Since we can’t discover every fact for ourselves, we look to competent authority for information and guidance.

We must accept large amounts of information which have accumulated over the centuries and we must accept much information from authorities around us in order to survive well in our society. We cannot personally check out everything. But we do need to be aware of potential problems connected with the appeal to authority.

We should, for instance, never surrender our own independent judgment concerning statements which can be true or false. We do need to put forth whatever effort is necessary to discover facts for ourselves and to challenge any authority we find suspect. Blind acceptance is a major problem in an appeal to authority.

When we are appealing to an authority as grounds for believing in a proposition, we should use the same qualification tests that are used to determine expert witnesses or authorities in a courtroom. Among these qualifications are:

  • Recognition of an authority by other authorities in the matter at hand. For instance, an authority should be recognized as such by members of the profession in which he claims competency.
  • The individual being judged as an expert or specialist should be identifiable. No unnamed authorities should be accepted.
  • The authority cited should generally be in agreement with other authorities who are expert in the same matter.
  • The authority should not be biased and we should try to determine if prejudices, biases, and stereotypes interfere with his judgment.
  • The cited authority should be living if his expertise depends on changeable information or he is working in a developing discipline, such as one of the empirical sciences. As we all know in this rapidly changing world, new evidence is discovered which may change our judgments, modify our theories, or challenge our current beliefs.

The Appeal to Reason

Sometimes we appeal to “reason” in an argument. Our reasoning faculty can be a source of true facts. What do we mean by reason? For our purposes here we will define reasoning as the process of using known facts to arrive at new facts. If we start with information we know to be true, we can arrive at new information we didn’t know by applying the procedures known as deduction and induction.

Deduction is the process of drawing specific conclusions from premises in a form known as a syllogism. To use deduction correctly, we need to know certain rules which enable us to make valid arguments. Mathematical reasoning is one form of deduction. But deduction can be used in every field of knowledge and in everyday arguments as well. It is a useful methodology but it can’t, of course, be used to derive all “truth.” Deduction is one of the most important processes we will be concerned with in our study of the science of logic.

Induction is the process of developing general hypotheses to account for a set of facts. We go from the particular to the general. We devise general principles and laws from specific cases. Induction gives us probable knowledge, but never certain knowledge. Nevertheless, scientific induction is a necessary and valuable procedure and we have all benefitted from its results. We will also be concerned with induction in our study of the science of logic.

We need to be aware of two dangers in reasoning. We should not think we can substitute deductive reasoning for empirical observation; deduction has its place but it is not a substitute for induction. Also, we should not consider inductive reasoning to be a source of certain knowledge; it can give us only tentative conclusions, subject to change as new knowledge is discovered.

The appeal to reason is closely related to the appeal to science. Science, as an organized body of knowledge, uses the reasoning process as its primary methodology. Since so many of our public policies are dependent on scientific knowledge and appeals to science are heard so often in news reports, let’s consider it separately.

The Appeal to Science

A day hardly goes by that we don’t see or hear something similar to the following: “According to new scientific information…” the following should be accepted as true or false, or “Science now has shown that…” this is true or that is false. Many people think that an appeal to science is the strongest appeal to be made today. After all, science can’t be wrong, can it?

Before we tackle that question, we need to distinguish among the ways in which we use the term “science.” Generally speaking, a science is any organized body of knowledge. Philosophy and theology can be included in the concept of science in this sense, although in common use we may not include them. We can, furthermore, differentiate between a “formal” science and an “empirical” science.

A formal science is based primarily on deductive rules. Mathematics, logic, and library science are examples of a formal science. An empirical science is based primarily on empiricism (sense knowledge) and the inductive process. Chemistry, biology, and anthropology are examples of an empirical science.

We look to science for factual information and sound guidance. We appeal to scientific information as grounds to justify our propositions and our arguments. Can science ever be wrong? That is really the wrong question to ask and here’s why.

In a formal science, such as mathematics, we accept certain premises, axioms, assumptions, or postulates as being true. This, of course, is not done frivolously. There is usually a good reason to accept them as true. From these very basic premises, accepted as true, further premises are generated and conclusions are drawn inferentially. Assuming the inference has been valid, propositions drawn from initial premises can be said to be true.

In an empirical science, such as chemistry, we accept propositions to be true if the inductive process used confirms them to be true. But the “truth” of these propositions is always tentative, never certain, although we may have strong evidence (the weight of the evidence; do you recall this?) to support the propositions. The propositions made by empirical science are always subject to change, although many of the propositions are so weighted in favor of their being true that we generally don’t doubt them at all.

The Appeal to Intuition

Now and then we encounter someone who appeals to intuition as a grounds to support some proposition in an argument. We can define intuition as the process by which insights or bits of knowledge emerge into consciousness from the subconscious or as the direct apprehension of knowledge which is not the result of conscious reasoning or immediate sense perception.

There are two major problems with appealing to intuition in an argument. First of all, intuitions are private and cannot be verified; they cannot be subjected to any public test and, therefore, do not provide convincing evidence in an argument. Secondly, the insights produced by intuition are as likely to be wrong as they are to be right. By itself alone, intuition is not a safe method of obtaining knowledge. There is no way to publicly verify a proposition grounded in an intuition. The best thing to do is leave intuitions out of your arguments.

The appeal to intuition is related to the appeal to revelation. The major difference between the two is that in intuition the source of the claim comes from inside us, whereas in revelation the source of the claim comes from a “supernatural” being.

The Appeal to Revelation

Supernatural revelation has been accepted as a source of knowledge and as a source of evidence for as long as man’s known history. All sorts of knowledge have been attributed to the gods or to God. The appeal to revelation as grounds in an argument is loaded with problems.

How do we independently verify that the knowledge from revelation is true? Revelatory knowledge can’t be put out in the public arena and justified by appeals to sense perception, deductive or inductive reasoning, or any other test of truth. It has more in common with “intuition” than with other sources of knowledge.

Even noting that the appeal to revelation is important for millions of people, the fact is that propositions from this source of knowledge have no way of being verified as true. The basis for believing propositions from supernatural revelation is “faith,” and faith, by necessity, is a private affair, not subject to the same standards of truth as other sources of knowledge for which public verification is possible.

The above is not meant to disparage revelation as a source of private knowledge. Millions of people have found comfort and personal enlightenment in the doctrines provided by what is claimed to be divine revelation. The point is that no doctrine provided solely by revelation can be tested publicly and, therefore, does not have and cannot have the status of propositions or arguments for which publicly verified claims can be made.

Other Sources of Knowledge for Which Claims are Made

There may be other sources of knowledge for which we don’t have adequate evidence at the present time. Fact-claims for these sources of knowledge are weak and caution should always be used in dealing with people who make claims based on them. We should not allow claims made on the basis of these sources to enter our arguments. Some of these sources for which claims are made or have been made are listed here.

Extrasensory Perception

Most of us seem to be intrigued by ESP. Many people claim to have had experiences of telepathy, clairvoyance, or precognition. Although there are ongoing experiments being conducted with ESP, the final word is not in yet. We should, therefore, be cautious about claiming that any proposition is true based on extrasensory perception. We should avoid using such propositions in our arguments and should be wary of others who may use them in their arguments.

Racial Memory

There are some who claim that there is a “collective unconscious” which we inherit as human beings and is a source of knowledge. This doctrine was developed by the famous psychologist Carl Jung and has been popularized by many others. Unfortunately for the supporters of this doctrine of “racial memory,” there is at this time no objective evidence supporting such a claim.


Anamnesis refers to a recollection or remembrance of things from a previous existence. Some books and movies have popularized this alleged phenomenon. The problem with it is that there is at the present time no way to verify its existence nor to verify any propositions based on it as a source of knowledge.

The Occult

Astrology, spiritualism, Tarot cards, Ouija Boards, and such occult sources are commonly believed to give us certain kinds of information. It is surprising how many people believe in such sources. There is, however, no objective evidence supporting the claims of occult sources. Horoscopes, for instance, have been consistently unreliable as a source of true information and many of them are written so generally that the statements included in them could be interpreted in numerous ways.

In Defense of Common Sense Realism

Before we leave this subject about the sources of knowledge, it might be advisable to return to the matter of common sense realism and consider some additional notions regarding it.

It has been fashionable in many quarters, particularly academic, to downplay common sense as if it wasn’t at all important at best and downright devious and damaging at worst. Common sense as a source of knowledge has come under attack and it’s been said that common sense cannot be depended upon as an adequate and “true” source of knowledge.

There is no doubt that some claims made on the basis of common sense opinion have been shown to be false. Surprisingly enough, however, when challenged to cite examples, the academics and intellectuals cannot provide very many mistaken claims based on common sense.

Let’s make this clear. Human beings have believed things based on common sense opinion which have turned out to be untrue. Fortunately for us, these claims have been relatively small in number. Otherwise, human beings may have perished long ago.

What needs to be said is that common sense opinion accepted without appropriate criticism and analysis may lead to false claims. We must, of course, be willing to give up a claim thought to be true if evidence is found that shows it to be untrue. This is why we should really speak of common sense critically examined.

Let’s consider an example of a claim based on common sense, which was once thought to be true, and was later shown to be false. People once believed that the sun revolved around the earth. Was this a reasonable belief of common sense?

Tomorrow morning, before the sun comes up, go outside and direct your attention to the east. Watch now as the sun rises above the eastern horizon and begins its course across the sky. Later in the day, go outside to watch the sun descend into the western horizon. Get up the next day and do the same. Do the same for the next year.

Now suppose you know nothing about the rotation of the earth and the orbits of other bodies within our solar system. You have seen (the source here is sense perception) the sun arise in the east and settle in the west. You have watched this same phenomenon for a year. It is always the same. The sun comes up in one direction, travels across the sky, and settles in the opposite direction as it disappears from view.

Based on what you have experienced, what conclusion do you draw? (Remember you know nothing about the rotation of the earth!) Of course, the conclusion drawn is that the sun must be going around the earth. This is only common sense. And it was common sense for centuries. It was a reasonable conclusion concerning the knowledge available at the time.

We know now that the statement, “The sun travels around (orbits) the earth,” is not a true proposition. We know that the earth travels around or orbits the sun. Observations, experiments, and critical analysis show that this is the true proposition. So . . .

Go outside tomorrow and observe the sun rising in the east and settling in the west. What appears to be the case? You know the earth is really traveling around the sun. But how does it appear? You are seeing the same thing that men have seen for centuries. The phenomenon you perceive is the same that they perceived. What is different? Only the judgment that you make compared to the judgment they made. You have additional knowledge. You know the earth rotates and you know the earth orbits the sun.

The phenomenon remains the same. Only the conclusion drawn is different. What was common sense at one time has given way to common sense critically examined and based on new evidence. That the earth orbits the sun is now common sense. But it’s merely updated common sense. Keep in mind that our language still hangs on to the original proposition based on the old common sense. We still say, “The sun will rise in the east,” and “Let’s go outside and see the beautiful sunset as the sun descends into the west.” We know, of course, that the sun does not rise in the east and set in the west. But isn’t it romantic to say that it does? The language may not be strictly scientific, but there’s nothing wrong with a little poetry in our lives.

There is nothing wrong either with common sense as a source of knowledge and, for the most part, it seems to be our main source of knowledge. Most of our common sense propositions are based on sense perception, empirical experiences, and reasoning, either deductive or inductive. These propositions are then passed on to us by those in authority: our parents, teachers, and others. What we need to be wary of is just accepting a common sense statement at face value without examining it.

In a way, all knowledge and reflection on that knowledge really begins with common sense. Our accumulated sense perceptions and their formation into ideas, propositions taught to us by our first and primary authorities such as parents and other members of the family, and the sum of what we are taught by society and inherit from our culture, are all related in a real way to common sense as a source of knowledge.

Common sense, therefore, should be embraced, not discarded. But it is always possible for us to “inherit” a common sense proposition that is false. The answer to this situation is to examine any questionable proposition critically and submit it to all the tests possible to determine its veracity. And here we really need the tools provided by the science of logic, philosophical analysis, and empirical science.

A great philosopher once said: “The unexamined life is not worth living.” We, as students of philosophy and logic, may want to join in a statement made by another great philosopher of the past: “The unexamined proposition is not worth believing.”

Dr. Jonathan Dolhenty was the Founder and President of The Center for Applied Philosophy and the Radical Academy, and is Honorary Philosophy Editor at The Moral Liberal. The Moral Liberal has adopted these projects beginning with a republishing and preserving of all of Dr. Dolhenty’s work.

The Moral Liberal recommends: Great Books of the Western World