For the philosopher, the mind is the laboratory. Here are some examples of valid reasoning tools you can apply to your thinking, and also some invalid tools or fallacies to watch out for when reading or listening to others such as ministers, politicians, lawyers, journalists, scholarly debaters, or salespersons.
Valid Reasoning Tools (Logic):
Logic - The study of the methods or reasoning and argumentation or the formal methods of valid reasoning.
1. Deductive Reasoning - The process of starting with a general statement and arriving at a specific conclusion. When a valid method (form) is used, the conclusion will be true if the starting statement (premise) is true.
example: Living things can exist only where there is oxygen. There is evidence of past living things on Mars, so therefore, Mars once had oxygen.
Syllogism - A form of deductive reasoning with two premises (major and minor), one conclusion, and which uses the terms "all" or "none".
example: All planets in our solar system revolve around the Sun. Mars is a planet in our solar system; therefore, Mars revolves around the Sun.
2. Inductive Reasoning - The process of starting with a specific statement and arriving at a general conclusion. When a valid method (form) is used, the more truthful the starting statement (premise) that is used based on experience, the more probable the conclusion can be expected to be true.
example: All of the planets we have observed in the universe revolve around a star; therefore, to discover more planets, we must begin with locating other stars.
Analogy - A comparison of two things based on the assumption that if they are known to be alike in some respects then they are alike in other respects.
example: John is successful because he enjoys his work. Tom enjoys his work, so he will probably be successful.
Causal Connection - A conclusion that infers what was likely to be the direct cause of an observed effect.
example: The craters on the moon were probably made by falling meteors.
3. Mathematical Logic - The use of symbols to represent words in a logic process so that it has a more mathematical nature.
example: A (AB)B represents If A is true and A implies B, then B is true.
Invalid Reasoning Tools (Fallacies):
Fallacy - An erroneous argument based on either a false starting statement (premise), a false supporting statement, or a deceptive or faulty logic method (form) that can result in a false conclusion. Keep in mind that fallacies can be highly effective if the reader or listener is not reasoning well.
1. Questionable Premise - To make a premise or starting statement to an argument that is inadequately supported.
example: A politician claims a particular program is needed, then makes a persuasive speech about how to fund the program without explaining why the program is needed.
2. Questionable Cause - To state that something is the cause of a particular result without presenting sufficient evidence for it.
example: A politician claims that crime went down soon after he enticed new businesses to move into the area.
3. Questionable Analogy (False Comparison) - To make specific comparisions that lead to false conclusions about dissimilar persons, groups, or objects.
example: A minister claims that persons who don't revere God are like people who lack respect for their parents.
4. Questionable Classification - To incorrectly label or classify a person or group based on one action rather than their consistent pattern of actions.
example: A politician claims that his opponent is a "big spender" because the opponent favors one particular program.
5. Suppressed Evidence - To make or accept an argument in which only the evidence favorable to one side or position is given, and the opposing view is not addressed.
example: A businessperson claims that her product contains a special active ingredient and that no other product is better, but does not tell you that her competitor's product also contains the same ingredient and can perform equally well while costing less.
6. Generalizations - To make broad comparisions that lead to false conclusions about dissimilar persons, groups, or objects.
example: A minister states that parents who are not married are not good for children.
7. Inconsistency - To make contradictory statements to support a conclusion.
example: A minister states that love and peace are to be highly valued, but then uses warlike language and intolerance toward persons or groups of a different religion.
8. Irrelevance - To use evidence that is highly unrelated to the analysis of the premise.
example: A lawyer states that her client (defendant) is a model citizen and not capable of causing an automobile accident.
9. Begging The Question (Circular Reasoning) - To quickly yield to or endorse a position in question without providing any supporting evidence, or to presuppose the conclusion in a argument.
example: A person claims that a politician who holds a particularly different view on an issue should not be in office, rather than explaining why he disagrees with the politician.
23. The fallacy of Composition is committed when a conclusion is drawn about a whole based on the features of its constituents when, in fact, no justification provided for the inference. There are actually two types of this fallacy, both of which are known by the same name (because of the high degree of similarity).
The first type of fallacy of Composition arises when a person reasons from the characteristics of individual members of a class or group to a conclusion regarding the characteristics of the entire class or group (taken as a whole). More formally, the "reasoning" would look something like this.
1. Individual F things have characteristics A, B, C, etc.
2. Therefore, the (whole) class of F things has characteristics A, B, C, etc.
The second type of fallacy of Composition is committed when it is concluded that what is true of the parts of a whole must be true of the whole without there being adequate justification for the claim. More formally, the line of "reasoning" would be as follows:
1. The parts of the whole X have characteristics A, B, C, etc.
2. Therefore the whole X must have characteristics A, B, C.