Introduction to Logic - Ch. 1

(Originally written September 5, 2006 in Book 9)

Introduction to Logic
Harry J. Gensler

Harry J. Gensler is a professor at John Carroll University. HE thanks my professor of Logic at Taylor University, Winfried Cordon for suggestions and encouragement

Chapter 1 - Introduction

'Logic is about reasoning" (Gensler, 1)

Logic - the analysis and appraisal of arguments

It is a tool that we can use in every day life and deep philosophical issues.

Why study logic?
-Logic can be fun
-Logic can deepen your understanding of philosophy
-Logic can improve your analytical skills

Philosophy - reasoning about the ultimate questions of life

Valid arguments:

Premises - given information

Conclusion - outcome of the premises

Argument - a set of statements consisting of premises and a conclusion. Normally, the premises give evidence for the conclusion.

Valid Argument - an argument that if it would be contradictory or impossible to have the premises true and the conclusion be false.

A valid argument does not necessarily mean that the conclusion is true, only that the conclusion is logically flowing from the premises. A valid argument states that if the premises are true, the conclusion will be true.

Logical form - correct usage of logical notions ("if-then" and "not") and content phrases ("You overslept" and "You're late")

Argument/(Form)

1. If you overslept, you'll be late (If A then B)
2. You aren't late (Not-B)
Therefore, You didn't oversleep (Therefore, Not-A)

If the form is correct the argument is valid.

Valid:

If A then B
Not-B
Therefore, Not-A

Invalid:

If A then B
Not-A
Therefore, Not-B

It is invalid because it does not follow the correct form.

Sound Arguments

"An argument is valid if it would be contradictory to have the premises all true and conclusion false. An argument is sound if it's valid and has every premise true" (Gensler, 4).

Sound Argument - A valid argument that has true premises

To prove something we try to offer a sound argument. A sound argument must meet two criteria:
1) The premises must be true
2) The conclusion follows from the premises

An argument is unsound if it does not meet one of these required criteria.

When we criticize an opponent's argument we attempt to prove that the argument is unsound.

We ask ourselves how certain our premises are. An argument is only as strong as the premises of an argument.

Another way to attack an argument is to call a premise's certitude and obviousness into question.

Logic can clarify discussion about philosophical topics. It is an intellectual tool to reason better about deep issues.

Statements can be true or false, not valid or invalid. Arguments will be called valid or invalid, not true or false.

The plan of this book:
Ch. 1 - Brief intro to logic
Ch. 2 - Syllogistic logic, an ancient form of logic
Ch. 3-6 - Classical systems of modern logic
Ch. 7-10 - advance and controversial systems of philosophical interest
Ch. 11 Ethical formalization
Ch. 12 - Metalogic
Ch. 13 - Inductive Logic
Ch. 14 - Meanings and definitions
Ch. 15 - informal fallacies