CPSP118G Fall Semester: Earth, Life & Time Colloquium

Logic and Logical Fallacies: Reasonable and Unreasonable Approaches to Thinking

Thomas R. Holtz, Jr.

From the Greek logos, word, logic can be defined as the study of principles and rules to arrive at correct reasoning. It works primarily by the reasoning together of and statement of arguments. NOTE: popular use of the term to the contrary, in logic and rhetoric an "argument" is NOT simply contradiction, the "automatic gainsaying of any statement the other person makes." Instead, an argument is a connected series of statements intended to establish a proposition.

In other words, to "argue" is to "state one's case".

There is a vast field of formal logic with its own sets of technical terminology, symbols, etc. What we will present is greatly reduced.

The each individual statement in the "series of statements intended to establish a proposition" is called a premise. An argument might have a single premise, although many have a series of premises. In a properly constructed argument, the premise(s) should support a conclusion, the proposition which you were trying to establish.

Logic is used (or at least is used in principle) in nearly every field of human endeavour: science and other academic fields (history, etc.), of course, but also politics, business, advertising; indeed, anytime that someone is trying to convince other people about some proposition.

However, not all arguments are well-constructed. Logical fallacies can be unintentional (due to, among other things, Kida's 6 basic mistakes we make in thinking), or they can be quite deliberate. In the latter case, they are used as rhetorical devices to convince others instead of using correct, sound, valid reasoning.

The following is a sampling of some of the more commonly-encountered logical fallacies. There are many more. Also, some of the ones listed below go by many different names (in fact, most of these have Latin names as well). Additionally, some of these shade into each other. We've grouped these into general categories.

Some final thoughts on logical fallacies:

Last modified: 17 September 2008