The Basics of Logical Argument

Two Kinds of Argument The Deductive argument: true premises guarantee a true conclusion. e.g. All men are mortal. Socrates is a man. Socrates is mortal.

Two Kinds of Argument The Inductive Argument: the premises only make the conclusion probable. e.g. The sun will rise tomorrow. It always has.

Two Kinds of Argument In debate, then, most arguments are inductive. Frequently, truth is too high a mark to attain, and the best the arguer can claim is reasonableness.

Good Premises: 3 Criteria Practical logic is about evaluating premises, and the inferred conclusion they are supposed to support. Premises are good if theyre relevant, sufficient, and acceptable.

Good Premises: 3 Criteria 1. Relevance The premises offered in support of the conclusion must have some relation to that conclusion.

Good Premises: 3 Criteria For example, if someone were to argue that, because our winters are cold and snowy, we should join the U.S., they would be connecting 2 things that have no direct relationship.

Good Premises: 3 Criteria 2. Sufficiency Taken together, the premises must provide enough evidence for the conclusion.

Good Premises: 3 Criteria For example, the failure of one student to be in code is clearly relevant to the question whether students are open to school uniforms - but doesnt prove anything.

Good Premises: 3 Criteria 3. Acceptability The arguer must convince us to accept that they are offering reasonable premises.

Good Premises: 3 Criteria For example, many people still cling to the idea that Elvis Lives!, though their evidence is nothing more than speculation. This is an instance of unreasonable belief.

Logical Fallacies When an argument is flawed or weak because it violates one or more of these three criteria, we call it a fallacy. Studying fallacies helps you spot others bad arguments and form good ones yourself.