Criteria of Truth
One important area of logic is concerned with tests of truth - the criteria used to distinguish truth from error. A criterion of truth is a standard, or rule, by which to judge the accuracy of statements and opinions; thus, it is a standard of verification.
To obtain a clear, correct view of any philosophy, one must understand its criteria of truth. This is particularly the case because of the many conflicting ideas to be found in different philosophies. The laws of logic cannot of themselves disclose facts about the world of man or nature. In order to discover such facts, or to evaluate the content of an argument, the individual must decide upon the criteria which can enable him to distinguish what is true from what is not true.
Not all criteria have equal validity or value; while some are adequate, others are of questionable worth. The criteria dealt with in the present discussion have been chosen, not necessarily because they may be widely regarded as most useful or adequate but rather because they have become most familiar to, and are in common use among, the general public and academic or scholarly circles.
Custom. Many persons either knowingly or unwittingly employ custom as a criterion of truth, assuming that doing what is customary will not lead them too far astray. The admonition, "When in Rome, do as the Romans do," expresses an appeal to custom as a criterion, particularly in matters involving the determination of moral truth. Thus people adhere closely to custom as a criterion when they dress as others dress, use expressions which are in vogue, practice moral principles currently approved -in other words, do whatever is popular.
Custom scarcely merits serious consideration as a criterion of lruth. Surely, a scientist oblaining evidence of facts or principles. could never accept conflicting customs of majorities, or of minorities either, as a test. A public opinion poll can never be the best way to determine scientific truths.
Tradition. Closely allied to custom as a proposed test of truth is tradition, the notion that what lasts for generations must be valid. Those who accept tradition as a criterion may defend their view on the ground that any practice which has gained the loyalty of succeeding generations must deserve a measure of credibility.
The same objections to custom as a standard of truth apply to tradition as well. Many traditions merely repeat what is false (consider, for example, the innumerable false traditions of primitive tribes) and, moreover, traditions often conflict with one another. It is clear that science cannot accept tradition as its test of truth.
Time. Perhaps you have heard some person in a debate appeal to time as the test of truth, arguing with statements such as, "My belief has stood the test of time," or "Christianity must be true, for . it has stood the test of time." The logic of such argument is based on the assumption that if a belief is really erroneous, the error will sooner or later come to light, whereas, if there is nothing wrong with the belief, the mere passage of time cannot destroy its validity.
Time is not an adequate test of truth. It is closely related to custom and tradition, which, in fact, are simply aspects of the time factor. The inadequacy of time as a criterion becomes apparent if we note that many errors have lasted for a very long time before being exposed as errors. The most absurd superstitions have endured throughout generations, centuries, even millenia. Surely, modern peoples who believe in the truth of a great religion, such as Christianity, would not give up their beliefs and change to some other system of religion which happened to be hundreds or perhaps thousands of years older than their own religion.
Feelings (Emotions). Many individuals faced with the necessity of making a decision allow their emotions to sway them despite contrary evidence or without even attempting to obtain and evaluate evidence. Such people are implicitly accepting emotions as a test of truth. Too many depend upon subjective feelings as a guide to a great variety of situations, ranging from trivial problems of everyday living to the most serious problems of the community.
Most people today, however, will admit that they cannot trust their emotions in important matters. Thus the experienced business executive ignores his feelings and searches for facts when making investments. The scientist, physician, historian, and scholars in other fields have similarly learned to ignore subjective reactions of this kind.

Instinct. The existence of separate instincts has long been in dispute. Instinctive behavior may be regarded as akin to feeling, or perhaps as a universal mode of feeling. From this point of view, it is the instinct of thirst that impels us to drink, the instinct of hunger to eat, etc. Some have gone so far as to assert that even the existence of God can be proved by reference to instinct, arguing that all instincts have their corresponding objects in the world of reality. Thus the corresponding object for the thirst instinct is a liquid; for the hunger instinct, food; f-or the sex instinct, a mate. The argument therefore concludes that, since all persons are religious, religion must be an instinct and its counterpart, God, must exist.
Instincts cannot be accepted as reliable tests: too often they are vague, ill-defined, variant and undependable, limited to specific types of activity. Even if we did accept instincts as valid tests, they are so few that we could not derive much evidence from them. To what extent could a scientist refer to them in his efforts to determine the composition of chemical substances?
Hunch. A hunch is an impulsive generalization, perhaps based on a vague or undefined notion. It can hardly be regarded as an acceptable criterion of truth, yet many persons confronted with a choice may allow a hunch to be the decisive factor. Hunches are closely related both to feeling and to intuition, another criterion discussed below.
Intuition. This criterion consists of judgment without recourse to reasoning from facts; it is an assumed truth issuing from an unknown or unexplored source. Many persons gain intuitive insights which later prove to be true. Some scientists, without employing the rational cognitive processes of the mind, hit upon a useful hypothesis or proof while merely resting, daydreaming, or doing other things which have no apparent relationship to the truths they are seeking to discover.
Intuition as a criterion of truth suffers from two major objections: (1) It is not available when needed; it cannot be depended upon in given situations in the same or at least similar manner that reason may be employed. (2) Intuitions are, at best, potential sources of truth, not tests; when a person claims to have an intuition, he should immediately test it in order to determine whether it is true or false.
Revelation. The main difference between intuition and revelation is the fact that the source of intuition is unknown, whereas the source of revelation is assumed to be God. Revelation may be defined as a truth or disclosure which emanates from God. Many religions rely heavily upon the validity of revelation as a criterion of truth.
The adverse criticism stated above in regard to intuition holds good for revelation as well. When a person possesses what he claims to be a revelation, it is incumbent upon him to prove it, and the standard to which he appeals as the test consequently becomes his criterion. An individual may accept revelation as a source of some truths, but he cannot depend on such experience as a means of demonstrating to others the validity of his beliefs.
Majority Rule. The criterion of majority rule is a statistical basis for the acceptance of assertions or proposals. In democratic countries and organizations, majority vote is accepted by all members of a group as a guide to joint decisions. This is particularly true during enactment of laws pertaining to personal morality and social behavior. Often, however, a democratic community, divided into several opposing factions, must be content with a mere plurality.
Although a majority vote is good democratic procedure, it is not the best system for determining truth. Think what would happen if a scientist tried to arrive at conclusions by means of a majority vote-if, for example, an astronomer took a vote among the general population to ascertain whether assertions about the planets or stars were to be accepted as true or rejected as false.
Consensus Gentium. There are those who believe that the opinions held in common by all people comprise an acceptable criterion of truth. Consensus gentium, the unanimous opinion of mankind (universal or general consent), is believed to have a validity which is not to be found in majority decisions. According to this criterion, the fact that all human beings adhere to a given belief proves it to be necessarily true.
There is some cogency in consensus gentium if it means a universal innate truth such as the principles of logic and mathematics, but if it means merely general assent, as reflected by a unanimous vote cast in favor of a given decision, its value is questionable. General assent proves little-thus, at one time the masses believed that the world was flat and that the sun revolved about the earth.
Naive Realism. According to Naive Realism, things are in reality as the senses depict them. Human sense organs determine the truth or falsity of objects and conclusions. Only that which is subject to first-hand observation is verifiable. The expression, "I'm from Missouri, I have to be shown," exemplifies this criterion, the idea being, "Unless I see it, I will not believe it."
Naive Realism is an inadequate criterion of truth; for example, scientific truths are often beyond the scope of the senses. X rays, light waves, chemical reactions, and a host of other natural phenomena cannot be sensed, though they are understood and demonstrably real. Naive Realism as a valid test of truth would impel us to conclude that a straight stick in water is actually bent because it appears bent to our sense of vision. Sounds with a wave frequency above 20,000 cycles per second can be detected indirectly even though man's auditory sense does not reveal them. Furthermore, sense experience can be quite illusory; for instance, six pencil points touching a person's small of the back (remaining within the two-point threshold) are sensed as only one and Naive Realism would compel us to conclude erroneously that this sense experience is correct.
Correspondence. The criterion of correspondence states that an idea which agrees with its object is necessarily true. Thus the statement that the White House is situated in Washington, D.C., is true if the fact as to its location corresponds with the idea in the statement.
Correspondence appears to be the best of the criteria presented above-and many philosophers consider it to be the most valid of all tests of truth-but, like the rest, this criterion is sub. ject to adverse criticism. Granted, an idea which corresponds to its object is indeed true, but how can one determine whether or not his idea does in fact bear a perfect correspondence to its object? To make this determination requires the use of some criterion other than correspondence. But if another test of truth has to be applied, the correspondence criterion becomes merely a definition of truth, not a decisive test. In other words, besides asserting correspondence between an idea and reality, we still need to apply a test that will disclose the precise degree of similarity between what we think and what actually exists.

Authority. Often the opinions of highly trained men who have achieved a degree of success in a given area of specialization are regarded as acceptable evidence or proof. These specialists, or authorities, can be relied upon because of their acquaintance with and mastery of a particular subject. They are admittedly capable of reasoning with accuracy in matters in which they are regarded as expert; consequently, their proposals command respect and their statements are accepted as criteria of truth. However, a person cannot merely pose as an authority in an iPse dixit (I myself said so) manner, but must be duly qualified.
Although authority is often a particularly good criterion of truth-one that is widely and effectively used (e.g., in a court of law)-this criterion is far from being final, for in many instances two noted authorities may give contradictQry evidence.
The Pragmatic Criterion of Truth. To the Pragmatist, if an idea works, it must be accepted as true. In other words, the workability of an idea determines its truth. From the consequences which issue from a given idea, its truth is obtained or measured. Since ideas produce results, examination of the results will either verify or disprove the ideas themselves. The full meaning of an idea is to be found in the consequences which follow from its application; thus, the results of the administration of penicillin to cure bacterial infection will prove the validity and disclose the significance of the statement that the drug is an effective therapeutic agent.
Although Pragmatism offers a most valuable criterion of truth, the criterion must be viewed with reservations and used with caution. Not all ideas that appear to be working are true; for example, a physician who apparently cures a patient's neurosis by prescribing a given medicine and accepts it as a remedy may later discover that the use of a placebo (innocuous medication) which resembles the original medicine works equally well. He may be compelled to admit that the medication was not effective and that his initial judgment was incorrect: (Perhaps psychic experience or faith effected the cure.) Such instances indicate that untru ideas may seem to be working in practice contrary to the pragmatic test.
Nevertheless, there is definite validity in Pragmatism as a criterion, at least that kind of validity characterized (by William Ernest Hocking) as Negative Pragmatism. In brief, this principle states that, if an idea does not work, then it cannot possibly be true, for the reason that the truth always works (even though at times what appears to be working mayor may not be true).
Loose (or Mere) Consistency. Correct, but not necessarily related, statements are said to be consistent if they do not contradict one another. (Similarly, an individual is consistent in so far as he does not contradict himself.) Thus, consistency is attributed to the following statements because none of them negates any of the others: "Snow is white." HA ton of lead is heavy." "Yesterday the temperature dropped to twenty degrees." "George Washington was the first president of the United States."
The inadequacy of loose consistency as a criterion of truth is readily detected because the consistent statements are disconnected and lack cohesiveness or integration. The value of proof lies in its relationships which integrate isolated data into a coherent whole.

Rigorous Consistency. The criterion of rigorous consistency refers to connections between statements such that one proposition follows necessarily from another. Mathematical and formal logical reasoning exemplify this criterion. Examples are: "If all generals in the U.S. Army are also soldiers, and if john Doe is a general in the U.S. Army, then it follows necessarily that john Doe is a soldier." "If all A's are B's and all B's ar:e C's, then all A's are C's."
The value of rigorous consistency is to be granted; however, the areas to which this form of reasoning is applicable are limited. Furthermore, the premises are taken for granted; that is to say, to establish their accuracy requires another criterion of truth.
A further objection states that despite rigorous consistencYI a set of philosophical conclusions may display lack of coherence. Moreover, a system of philosophy may be rigorously consistent with only those facts which it has included for consideration, whereas an adequate criterion must take all facts into consideration, whether or not the new data are detrimental to the system in question.
Coherence. As a criterion of truth, coherence refers to a systematic consistent explanation of all the facts of experience. To be coherent, a person must arrange all pertinent facts so that they will be in. proper relationship to one another consistently and cohesively as parts of an integrated whole. Whatever facts are brought to light must be explained, must somehow be fitted into the system as a relevant or integral part. That explanation which most fulfills the requirements of coherence may be regarded as adequately verified.
Of all the criteria treated, coherence meets the demands of a standard of verification or test of truth most adequately. It includes reason, facts, system, integration, relationships, consistency. Its obvious limitation lies not in the criterion of coherence, but in man's limitations or his inability to obtain all facts of experience. Only an omniscient mind possesses all facts of experience; consequently, man must be content to deal with all facts at his disposal at the present time, allowing that point to be regarded as proved true which is the most coherent under prevailing circumstances. That person, school of thought, or idea which is supported in a coherent manner by most of the facts must be accepted as verified.
One who objects to coherence as a criterion places himself in a delicate position logically, for he thus implies a preference for incoherence, which is absurd; furthermore, to attack coherence necessitates the use of a criterion that is either coherent and rational, or incoherent and irrational; to appeal to irrationality is absurd, thus obligating a person to accept coherence as his criterion of truth.
Finally, a moot question arises as to whether or not there could be several equally coherent systems, each containing all the facts of human experience.
 

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