Logic has been defined as the study of the rules of correct thinking. It concentrates on the principles that guide rational thought and discussion. The most fundamental concept in logic is that of an argument. An argument must be distinguished from "arguing", which is a debate or disagreement between different people. The logical concept of an argument is: a set of statements, one of which is the conclusion , the others are premises, and the premises support the conclusion. In other words, it is a statement along with the evidence that supports it.

Logic plays a key role in philosophy. If there is going to be any rational discussion of different philosophical positions, the discussion must use the rules of logic. While logic will not specify what the content of the statements are, it will tell you how to arrange the statements in a logical fashion.

DEDUCTIVE ARGUMENTS

A deductive argument is one in which the conclusion is certain based on the premises. In a deductive argument the conclusion is contained in the premises.

INDUCTIVE ARGUMENTS

 An inductive argument is one in which the conclusion is probable based on the premises. In an inductive argument the conclusion goes beyond the premises.

 CATEGORICAL SYLLOGISMS

One of the earliest and most common forms of deductive logic was developed by the Greek philosopher Aristotle (384-322 B.C.). A categorical syllogism is a deductive argument containing three statements: two premises and one conclusion. Each of the three statements is a categorical statement. These statements can be of the form: All S are P, No S are P, Some S are P, or Some S are not P. An example of a valid categorical syllogism is:

ARGUMENT BY ANALOGY

A common form of inductive argument is the argument by analogy. This is an argument in which a conclusion is drawn about a situation based on similarities of this situation (analogies) to previous situations. For example, if we predict that a since it is snowing today a certain employee will be late because in the past when it was snowing the employee was late, we are making a probabilistic argument based on an analogy, the occurrence of snow.

MODUS PONENS

Here is a common form of deductive reasoning using the concept of a conditional or hypothetical statement. The name "modus ponens" comes from the Latin word "modus" meaning method, and the Latin word "ponens" meaning affirming.

 FALLACIES

Logic also discusses the incorrect ways of reasoning. A set of statements that appears to be an argument but is not is a fallacy. There are formal fallacies, which break specific rules of logic, and there are informal fallacies which usually are phrased to appear as an argument but the statements purporting to be premises to do not support the conclusion. One example of this is called a "circular argument", in which the conclusion is used as the premise.

Since "illegal" and "against the law" are the same concept, the speaker in the above fallacy is using the fact that counterfeiting is against the law to prove that it is illegal. In effect the speaker is just repeating the same statement two times. Nothing has been proven.

 Back to Home Page