Laws of Thought:
As we know that Logic is called the Science of the laws of thought or as a study of methods and principles which distinguish correct reasoning from incorrect reasoning. Now there must be the principles or laws which we study or which lie at the root of logic as a science. These principles or laws are called laws of thought. And because they underlie all valid or correct thinking they are called the foundations of Logic.
These fundamental Laws of Thought are:
The Law of Identity.
The Law of Non-Contradiction.
The Law of Excluded Middle.
The Law of sufficient Reason.
The Law of identity:
The law of identity says a thing is what it is; everything is identical with itself. Whatever a thing is, it is, and not another thing. A man is a man. A table is a table. A book is a book.
It is usually expressed by the formula, “If A is B, it is B.”
If iron is a metal, it is a metal; if man is mortal, he is mortal. Therefore if we say that a certain thing possesses a certain attribute we must always admit it throughout the argument. If we say board is black it must always be admitted that the attribute of blackness belongs to board. So the law of identity is an expression of identity of things.
It is important to note that this law says if in an argument we have used a term in certain sense we must use it in the same sense throughout the argument. Every term and proposition must be used in fixed meaning in an argument. No clear thinking is possible without identity. So this law demands that a term should have a fixed meaning in an argument.
The Law of Non-Contradiction:
This law says that a thing cannot both be and not be at the same time. It is expressed in the formula, “A cannot be both B and Non-B at the same time” two contradictory things cannot be true at the same time. A thing cannot posses two contradictory or inconsistent attributes at the same time and same place. A cannot posses the attributes of B and Non-B at the same time. A book cannot be red and non-red at the same time. A man cannot be Muslim and non-Muslim at the same time.
This law makes a negative statement. Two contradictory things cannot be true at the same time; one of them must be false. For example two contradictory statements ‘A is Muslim’ and ‘A is non-Muslim’ cannot be true at the same time. If A is Muslim then the statement ‘A is non-Muslim’ must be false. If the first one is true the second must be false and if the second one is true the first one must be false.
It must be noted here that it says that a thing cannot posses two contradictory attributes at the same time. It does not say that a thing cannot posses two different attributes at the same time. For example this law says that a thing cannot be black and non-black at the same time but it can be both black and bitter at the same time. Because black and bitter are not contradictory attributes but are only different attributes. The contradictory of black is non-black and of bitter is sweet.
The Law of Excluded Middle:
This law says that everything must either be or not be. It is expressed as, “A must be either B or non-B” it says A must posses one of the two contradictory attributes “B” or “non-B”. it says between the two contradictory attributes there is no middle course, there is no intermediate possibility. The middle is excluded. A colour must be either red or non-red. A man must be either Muslim or non-Muslim.
According to the Law of non-contradiction two contradictories cannot both be true at the same time; and this law says that two contradictory cannot both be false at the same time. In other words Law of non-contradiction says that two contradictory attributes cannot be present at the same time in a same thing while law of excluded middle says that two contradictory attributes cannot be absent at the same time in the same thing. So the former says two contradictory statements cannot both be true at the same time while the later says two contradictory statements both cannot be false at the same time. The Law of excluded middle is supplementary to the Law of non-contradiction.
Here again we must remember that the Law of excluded middle refers only to contradictories. For example we can say that a colour must be either red or non-red; but we cannot say that a colour must be either red or yellow because red and non-red are contradictories and between them there is no third possibility. But red and yellow are not contradictories rather contraries and between contraries other alternative is possible. So this law applies only in the case of contradictories and not in the case of contraries as we cannot say that if a colour not red it must be yellow; but we can say if a colour is not red it must be non-red.
The Law of Sufficient Reason:
This principle was first introduced by a German philosopher, Leibnitz in the words, “Nothing happens without a reason, why it should be so rather than otherwise”
Whatever exists or is true, must have a sufficient reason. Why this thing or proposition is as it is and not otherwise.
This law says that whenever there is anything it must have an adequate cause, there must be a sufficient reason behind it. So this law not only demands a cause for everything but sufficient reason or adequate cause. For example when we talk about the quantity of poison enough to kill a person we are actually talking about sufficient cause. And when we talk about the hard work which causes the success of a student we are talking about sufficient hard work not any amount of hard work.
So this law says that for everything there must be a sufficient cause or reason. If an earthquake happens there must be sufficient cause for its happening. Sometimes we might not be aware of the cause but it is not right to say that it happened by chance.
As we know that Logic is called the Science of the laws of thought or as a study of methods and principles which distinguish correct reasoning from incorrect reasoning. Now there must be the principles or laws which we study or which lie at the root of logic as a science. These principles or laws are called laws of thought. And because they underlie all valid or correct thinking they are called the foundations of Logic.
These fundamental Laws of Thought are:
The Law of Identity.
The Law of Non-Contradiction.
The Law of Excluded Middle.
The Law of sufficient Reason.
The Law of identity:
The law of identity says a thing is what it is; everything is identical with itself. Whatever a thing is, it is, and not another thing. A man is a man. A table is a table. A book is a book.
It is usually expressed by the formula, “If A is B, it is B.”
If iron is a metal, it is a metal; if man is mortal, he is mortal. Therefore if we say that a certain thing possesses a certain attribute we must always admit it throughout the argument. If we say board is black it must always be admitted that the attribute of blackness belongs to board. So the law of identity is an expression of identity of things.
It is important to note that this law says if in an argument we have used a term in certain sense we must use it in the same sense throughout the argument. Every term and proposition must be used in fixed meaning in an argument. No clear thinking is possible without identity. So this law demands that a term should have a fixed meaning in an argument.
The Law of Non-Contradiction:
This law says that a thing cannot both be and not be at the same time. It is expressed in the formula, “A cannot be both B and Non-B at the same time” two contradictory things cannot be true at the same time. A thing cannot posses two contradictory or inconsistent attributes at the same time and same place. A cannot posses the attributes of B and Non-B at the same time. A book cannot be red and non-red at the same time. A man cannot be Muslim and non-Muslim at the same time.
This law makes a negative statement. Two contradictory things cannot be true at the same time; one of them must be false. For example two contradictory statements ‘A is Muslim’ and ‘A is non-Muslim’ cannot be true at the same time. If A is Muslim then the statement ‘A is non-Muslim’ must be false. If the first one is true the second must be false and if the second one is true the first one must be false.
It must be noted here that it says that a thing cannot posses two contradictory attributes at the same time. It does not say that a thing cannot posses two different attributes at the same time. For example this law says that a thing cannot be black and non-black at the same time but it can be both black and bitter at the same time. Because black and bitter are not contradictory attributes but are only different attributes. The contradictory of black is non-black and of bitter is sweet.
The Law of Excluded Middle:
This law says that everything must either be or not be. It is expressed as, “A must be either B or non-B” it says A must posses one of the two contradictory attributes “B” or “non-B”. it says between the two contradictory attributes there is no middle course, there is no intermediate possibility. The middle is excluded. A colour must be either red or non-red. A man must be either Muslim or non-Muslim.
According to the Law of non-contradiction two contradictories cannot both be true at the same time; and this law says that two contradictory cannot both be false at the same time. In other words Law of non-contradiction says that two contradictory attributes cannot be present at the same time in a same thing while law of excluded middle says that two contradictory attributes cannot be absent at the same time in the same thing. So the former says two contradictory statements cannot both be true at the same time while the later says two contradictory statements both cannot be false at the same time. The Law of excluded middle is supplementary to the Law of non-contradiction.
Here again we must remember that the Law of excluded middle refers only to contradictories. For example we can say that a colour must be either red or non-red; but we cannot say that a colour must be either red or yellow because red and non-red are contradictories and between them there is no third possibility. But red and yellow are not contradictories rather contraries and between contraries other alternative is possible. So this law applies only in the case of contradictories and not in the case of contraries as we cannot say that if a colour not red it must be yellow; but we can say if a colour is not red it must be non-red.
The Law of Sufficient Reason:
This principle was first introduced by a German philosopher, Leibnitz in the words, “Nothing happens without a reason, why it should be so rather than otherwise”
Whatever exists or is true, must have a sufficient reason. Why this thing or proposition is as it is and not otherwise.
This law says that whenever there is anything it must have an adequate cause, there must be a sufficient reason behind it. So this law not only demands a cause for everything but sufficient reason or adequate cause. For example when we talk about the quantity of poison enough to kill a person we are actually talking about sufficient cause. And when we talk about the hard work which causes the success of a student we are talking about sufficient hard work not any amount of hard work.
So this law says that for everything there must be a sufficient cause or reason. If an earthquake happens there must be sufficient cause for its happening. Sometimes we might not be aware of the cause but it is not right to say that it happened by chance.
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