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Logic

The basic tool for effective thinking is logic. Logic is the science that investigates the principles governing correct or reliable inference.

The laws of thought are all reducible to the three following axioms, which are known as The Three Fundamental Laws of Thought.

  1. The Law of Identity
    Whatever is, is;
    or, in a more precise form,
    Every A is A.
  2. The Law of Noncontradiction
    Nothing can both be and not be; Nothing can
    be A and not A.
  3. The Law of Excluded Middle
    Everything must either be or not be;
    Everything is either A or not A.

More on the Three Laws of Thought

The law of identity states that A is A. An Apple is an Apple. In other words, something is what it is. If something exists, it has a nature, an essence. For example, a book has a front and back cover with pages. A car has four wheels, seats, doors, windows, etc. A tree has branches, leaves, a trunk, and roots. This also means that anything that exists has characteristics. We recognize what something is by observing its characteristic. You know that a tree is a tree because you see its branches, it’s leaves, its trunk, etc.

Furthermore, if something has an identity, it has a single identity. It does not have more than one identity. In other words, if something exists it has a set of attributes that are consistent with its own existence. It does not have a set of attributes that are inconsistent with itself. Therefore we can easily conclude that a cat is not a parachute. An Apple is not a race car. A tree is not a movie.

The law of noncontradiction tells us that A cannot be both A and not A at the same time and in the same sense. In other words, something (a statement) cannot be both true and false at the same time and in the same way. We use the law of noncontradiction constantly in discussions and debates because we are naturally able to recognize when someone is contradicting himself. If I were to tell you that yesterday I went shopping and then later I told you that yesterday I did not go shopping, you would be correct in saying there was a contradiction.

A contradiction occurs when one statement excludes the possibility of another and yet both are claimed to be true. Since we know that both cannot be true, we see a contradiction. From this principle, we can conclude that truth is not self-contradictory. This is a very important concept. Truth is not self-contradictory.

The law of excluded middle says that a statement is either true or false. For example, my hair is brown. It is either true or false that my hair is brown. Another example: I am pregnant. The statement is either true or false. Since I am a male, it is not possible for me to be pregnant. Therefore, the statement is false. If I were a female, it would be possible for me to be pregnant (given normal bodily conditions). A woman is not “kind-of” pregnant. She either is or is not pregnant – there is no middle position.

The law of excluded middle is important because it helps us deal in absolutes. This is particularly important in a society where relativism is promoted and truth statements are denied.

In Summary

1. The law of identity says that A is A, that if something exists it has a nature, a single nature.  It is what it is.

2. The law of noncontradiction says that A cannot be both A and not A at the same time and in the same sense. Truth is not self-contradictory.

3. The law of excluded middle says that a statement is either true or false.

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