Rules of Logic

W. P. Montague’s test for self-evident truths, as we noted in the last blog, involves the law of noncontradiction.  Rules of logic, such as this, provided us guidelines in our search for the truth.  As Trueblood states:

It is not intellectually honest to hold a position after it is known that the position leads inevitably to other positions which are recognized as false.  The respect for honesty involves, thus, the respect for consistency.  This presumably is accepted by all; if it is not accepted, intelligent discourse may as well come to an end. [1]

This rule tells us it is important to understand the implications of the positions we take because if we hold a position that involves a contradiction, we cannot expect others to take us seriously.  However, the law of noncontradiction is not an absolute test of truth.  Kant tells us this law can only tell us when two principles are in conflict but cannot tell us if those two principles are true.  Both principles could be false but not in conflict and the law of noncontradiction would not alert us to that fact. [2]  Our legal system provides an example.  There have been people convicted of a crime who later were proved to be innocent.  The jury convicted these people because they determined beyond a reasonable doubt the facts of the case proved the defendants were guilty and because they were of the opinion no major contradictions were present in the prosecution’s case.  Just because no contradictions are apparent does not indicate we have discovered a truth.

Lack of Knowledge

Both deductive and inductive logic can only work with the data the mind has.  Since humans are finite and have incomplete knowledge, logic will always work with incomplete data.  This means some of the conclusions reached by logic will be in error, not because of bad logic, but because of incomplete information.  It is an unfortunate part of the human condition that we will always make errors because our knowledge is limited; this has been and will be the cause of much human suffering.  Our medical science is proof of this.  Doctors do not know everything about the human body and diseases and as a result they do not have the knowledge and technology to heal all patients.  Any new technology represents a great number of unknowns and these unknowns can have tragic consequences.   For example, when engineers designed air bags for automobiles, they did so to protect human life and for the most part they succeeded.  However several young children have been killed by them because the engineers were limited in what they could foresee.  Aviation has had many accidents which have cost many lives but these accidents have taught us much about the technology of flying.  In spite of our lack of knowledge, humans are willing to pay the price to advance our knowledge.  We want to know the unknown and this desire, to a great extent, drives human progress.

An example of this human desire to know the unknown and the limits to logic is illustrated by the Dadaists who were a group artists and writers of the early 20th century.  These artists were horrified by the carnage of World War I and by what they considered to be the mechanical and rationalistic societies in which they lived.  In reaction, they deliberately stopped making sense.  The art they produced was nonsensical and highly experimental.  We should be able to understand their motive.  All of us should recognize that the mindset of the world—what is known—produces some of the horrors we see in our world and this should drive us to push on the boundaries of what is known in the hopes of finding a better way.


[1]   David Elton Trueblood, General Philosophy (New York:  Harper & Row:  1963), pp. 9-10.

[2]   Immanuel Kant, Critique of Pure Reason, ed. Mortimer J. Adler (Chicago:  Encyclopedia Britannica, Inc., 1990), p. 65.

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