Laws of Thought - Jim Berger's Zettlekasten

# Laws of Thought | | | | | |---|---|---|---| ||||| ||**Laws of Thought** (or Laws of Logic)||| ||||Logic| ||||| The **laws of thought** are fundamental axiomatic rules upon which rational discourse itself is based. The rules have a long tradition in the history of philosophy. They are laws that guides and underline everyone's thinking, thoughts, expressions, discussions, etc. The three classic laws of thought are attributed to [Aristotle](http://en.wikipedia.org/wiki/Aristotle) and were foundational in [scholastic logic](http://en.wikipedia.org/wiki/Scholastic_logic). They are: - [law of identity](http://en.wikipedia.org/wiki/Law_of_identity) - [law of noncontradiction](http://en.wikipedia.org/wiki/Law_of_noncontradiction) - [law of excluded middle](http://en.wikipedia.org/wiki/Law_of_excluded_middle) 1. **The law of identity**. The law of identity states that an object is the same as itself: A ≡A. For the [law of identity](http://en.wikipedia.org/wiki/Law_of_identity), Aristotle,[1] wrote: Now "why a thing is itself" is a meaningless inquiry (for—to give meaning to the question 'why'—the fact or the existence of the thing must already be evident—e.g., that the moon is eclipsed—but the fact that a thing is itself is the single reason and the single cause to be given in answer to all such questions as why the man is man, or the musician musical, unless one were to answer, 'because each thing is inseparable from itself, and its being one just meant this.' This, however, is common to all things and is a short and easy way with the question.) - _Metaphysics,_ Book VII, Part 17 2. **The law of non-contradiction** In logic, the law of non-contradiction ... states, in the words of Aristotle, that "one cannot say of something that it is and that it is not in the same respect and at the same time". (2) [note Aristotle's use of indices: 'respect' & 'time'] see the [Principle of contradiction](http://en.wikipedia.org/wiki/Principle_of_contradiction) 3. **The law of the excluded middle** Aristotle wrote that ambiguity can arise from the use of ambiguous names, but cannot exist in the "facts" themselves: It is impossible, then, that 'being a man' should mean precisely 'not being a man', if 'man' not only signifies something about one subject but also has one significance. … And it will not be possible to be and not to be the same thing, except in virtue of an ambiguity, just as if one whom we call 'man', and others were to call 'not-man'; but the point in question is not this, whether the same thing can at the same time be and not be a man in name, but whether it can be in fact. (Metaphysics 4.4, W.D. Ross (trans.), GBWW 8, 525–526). (3) Clipped on 13-January-2011, 10 : 00 AM from [http://en.wikipedia.org/wiki/Law_of_thought](http://en.wikipedia.org/wiki/Law_of_thought) **Liebniz's Law** The **identity of indiscernibles** is an [ontological](http://en.wikipedia.org/wiki/Ontology) principle which states that two or more [objects](http://en.wikipedia.org/wiki/Object_%28philosophy%29) or [entities](http://en.wikipedia.org/wiki/Entity) are identical (are one and the same entity) if they have all their [properties](http://en.wikipedia.org/wiki/Property_%28philosophy%29) in common. That is, entities _x_ and _y_ are identical if any [predicate](http://en.wikipedia.org/wiki/Predicate_%28logic%29) possessed by _x_ is also possessed by _y_ and vice versa. A related principle is the indiscernibility of identicals, discussed below. The principle is also known as **Leibniz's law** since a form of it is attributed to the German philosopher [Gottfried Wilhelm Leibniz](http://en.wikipedia.org/wiki/Leibniz). It is one of his two great metaphysical principles, the other being the [principle of sufficient reason](http://en.wikipedia.org/wiki/Principle_of_sufficient_reason). Both are famously used in his arguments with [Newton](http://en.wikipedia.org/wiki/Isaac_Newton) and [Clarke](http://en.wikipedia.org/wiki/Samuel_Clarke) in the [Leibniz-Clarke correspondence](http://en.wikipedia.org/wiki/Leibniz-Clarke_correspondence). Pasted from <[http://en.wikipedia.org/wiki/Identity_of_indiscernibles](http://en.wikipedia.org/wiki/Identity_of_indiscernibles)> Information provided by Jim Berger for your edification and viewing pleasure. | | == # The Three Laws of Logic SourceURL: [https://school.carm.org/amember/files/demo3/2_logic/3logic.htm](https://school.carm.org/amember/files/demo3/2_logic/3logic.htm) == | | |---| |**Three Laws of Logic**| | | |---| |Logic is the backbone of critical thinking. Logic is extremely useful for uncovering error and establishing truth. There are principles of logic and I would like to introduce you to the first three laws of logic. These are very important. 1. **The Law of Identity** 2. **The Law of Non-Contradiction** 3. **The Law of Excluded Middle** 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 leads, 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 non-contradiction 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 non-contradiction 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. Let me repeat it. 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. Please review these three laws and become familiar with them. They are extremely important when developing critical thinking skills. You will see them used throughout these upcoming lessons. **------------------------** **Focus Points** **------------------------** 1. The law of identity says that A is A, that if something exist it has a nature, a single nature. It is what it is. 2. The law of non-contradiction 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.| [[Laws of Thought.jpeg]] [[Laws of thought 2.jpeg]]