Objectives for Logic and More English Review (Weeks 2-3)

Why study logic? Students often begin this class saying all opinions — and especially ethical opinions — are equally legitimate. I do not think they really believe that, as a matter of practice. Students also argue for the merits of their favorite sports team, or musical group, for example. If all opinions really were equally legitimate, then a lunatic's opinions are as legitimate as anyone else's, and we simply cannot comment when the lunatic says aliens are sending him secret coded messages through bagels or dental fillings.

Some claims are simply not reasonable to believe. Note that I'm not saying the lunatic's claims are false; I am saying they're not reasonable to believe, given our other well-supported beliefs. They are inconsistent with our other well-supported beliefs. Once I begin to talk about consistency, I have begun talking the language of logic.

I would say some ethical beliefs are more reasonable to believe than others, simply on grounds of consistency. For example, if you want to keep children safe, you believe the claim "We should protect children" is true. If you believe that, then it would be inconsistent (not logical) of you to say it is also true that "If the kids in the WVC day care center want to play with loaded automatic weapons, we should provide them". This absurd example illustrates an important point: you cannot believe everything.

We are going to study the basic principles of logic, so you can see that some arguments really are better than others; and therefore, that conclusions of the better arguments are more worthy of belief than conclusions of worse ones.

To prepare for the logic test, see the file Study Guide for Logic Test.


Weeks 2 and 3 Basic Logic CM (all)
Critical Thinking Introduction
Study Guide for Logic Test
What is Bad Logic?
Refutation by Logical Analogy
Open and Closed Concepts and the Continuum Fallacy
The Fallacies of Composition and Division
What Are the Odds? Elementary Probability
Online Resources for Informal Fallacies
Self Test on Logic Concepts
Self Test on Fallacies
English review: Run-ons and Fragments Quiz 2 on English
English review: Singular-Plural Agreement
"e.g." and "i.e."
Quiz 3 on English

Some of the fallacies I have assigned are not discussed at much length in the Conway and Munson book.

Quibbling is also known as attack on a minor point. It's often a diversionary tactic in argument. For example:

Geometry Teacher: "Now we'll discuss circles." (Draws a circle on blackboard).

Student (quibbling): "That doesn't look like a circle to me. That's not a perfect circle. That's just one circle, and how can you generalize from that? That's not a circle at all; it's really just particles of chalk." Etc.

A sentence is objectionably vague if you can't tell what it says. Causes of objectionable vagueness include: ambiguity, equivocation, amphiboly, compatibility with all states of affairs, etc. Look at the samples in the file "How to Write Good".

Here is an objectionably vague paragraph:

"When looking at subjectivism in ethics, the focus needs to be on basic interpretations of all moral issues within an argument. Having validity or being classified invalid should not have any bearing on your assessment of a particular issue. After reading through Chapter 3, “The Elements of Moral Philosophy” by James Rachels, I became more aware of being able to consciously break down an issue through the different stages of the theory process." HUH?

Here are some links specifically for other fallacies:


Special Pleading (special pleading is a kind of inconsistency)

Poisoning the Well.
(Look under "P".)

Compatibility with all states of affairs (section 1)

Suggestion for Discussion Postings (online class only) / Class Discussion

As you study fallacies, you begin to notice them in ordinary life, especially in advertisements and political discussions. Share a "found fallacy."

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