Informal Fallacies

Sign In Quiz! Midterm Study Guide Inconsistency Ad Hominem Circumstantial Ad Hominem Genetic Fallacy Post hoc ergo propter hoc For next time: Read Chapter 7 pages 216-223

Quiz!

In one sentence, define the term 'inherent credibility'

Quiz!

A major car manufacturer has just hired Robert Downey Jr. to act as their spokesperson. In a recent commercial RDJ claimed that “diesel technology is no longer a dirty business.” What do you make of RDJ's claim?

(a) That RDJ is an interested party

(b) That RDJ is a legitimate authority in this domain

(c) That the claim has some inherent credibility based on your background beliefs and experience

(d) That appealing to RDJ is a fallacious appeal to authority

Quiz!

“If you eat something for lunch then you will be eating something during lunch” is an example of what kind of claim?

(a) A claim of value (b) A claim of irrelevance (c) A tautological claim (d) A contradiction (e) A syntactically ambiguous claim

Quiz!

(A): I have heard that you have failed to lower the unemployment rate in the last few years. Is that true?

(B): We have pumped billions into the local economy and we are doing everything possible to bring in more investments

This is an example of which fallacy?

(a) Belief Bias

(b) ad hominem

(c) red herring

(d) blue herring

Quiz!

When does a personal attack become an ad hominem?

Midterm Study Guide!

You now have your hands on the midterm study guide The Midterm is next Friday (October 28) If a topic or term is not on the study guide then it will

not be on the midterm Many of the questions will be slightly modified for the

midterm but not significantly (ex- argument diagrams) There is one exception: all of the IDs on the midterm

are on the study guide

IDs

The identification questions require at most 2 sentences

1. Define the term 2. Explain the significance of the term (why did we

study it?) Let's try an example: Semantic Ambiguity

Example

Semantic Ambiguity: When a claim has multiple meanings as a result of

the meaning of one the words in it. Semantic ambiguity is important because it can lead us to commit the fallacies of composition and division.

Ad hominems

We have discussed several distinctions having to do with critical evaluations of a source:

1. Personal attacks 2. Looking for interested parties 3. Ad Hominem attacks We said that ad hominem attacks occur only when

we criticize the source of a claim as a way of responding to the content of a claim

Ad Hominem types

We have already talked a bit about one of the most common forms of the ad hominem fallacy

The personal attack ad hominem But there are other ways in which we can criticize a

source as a way of responding to the content of a claim that do not include distinctly personal attacks

There is some overlap between fallacies like ad hominem and other fallacies

An ad hominem attack may also be a red herring

Inconsistency Ad Hominem

We commit the fallacy of the inconsistency ad hominem when:

As a way of responding to a someone's (or some organization's) claim we accuse them of contradicting themselves

– You claim that you care about the environment but didn't you fly over here in a big jet? Hypocrite!

An inconsistent person can make cogent claims and the simple act of having changed one's mind is not indicative of the soundness or strength of the arguments that they offer

Examples

(A) We need to make sure that everyone pays their fair share of taxes and the current tax rates are unfair.

(B) Didn't you cheat on your taxes last year? Why should I listen to you?

In this case A is being accused of believing that taxes should be fair but of unfairly evading taxation. This has little to do with whether A's claim is true

It is also an example of a red herring

Examples (more)

Images are not, strictly speaking, arguments in the technical sense

But this image also commits the inconsistency ad hominem fallacy

It does this by implying that Kerry's claims are not credible because of an inconsistency

Circumstantial Ad Hominem

We can also fallaciously question a claim's source by faulting a source's circumstances as the true reason for the claim

(A): The war on drugs is a hypocritical mess that needs to be ended

(B): You're just saying that because you want to get cheaper marijuana

Notice that B's response says nothing about A's claim but implies that A accepts the claim for personal or selfish reasons

Genetic Fallacy

A genetic fallacy includes any fallacy that casts doubt on a claim as a result of its history instead of its content

Ad hominem attacks are a kind of genetic fallacy. All genetic fallacies ignore the claim and focus on the source

For example: (A) We need to allow oil and gas exploration in the US

and the only way to do that is by relaxing environmental laws

(B) Isn't that a Republican policy? No thanks

Genetic Fallacy

The genetic fallacy, like ad hominem, is extremely common: (A) Public universities are a great resource (B) No they aren't, publicly owned institutions were first

built by socialist governments!

Whether or not the idea of state ownership of property (or services: police, fire, healthcare, etc) originated in one kind of government and economic system says little about the merits of those things today.

Post Hoc Ergo Propter Hoc

Post hoc ergo propter hoc is Latin for “after this therefore because of it”

We commit the fallacy of PHEPH when we assume a causal relationship exists between things just because one followed another

A happens then B happens

:. A causes B

The fact that A precedes B is not evidence that A causes B

In scientific reasoning this has a slogan: correlation does not imply causation!

Post Hoc Ergo Propter Hoc

Statistics have shown that days in which ice cream sales are high are also days with the greatest number of shark attacks. This implies that high ice cream sales are responsible for shark attacks.

Every time I have a cold I drink eight red bulls every day for three days. My cold disappears within a day or two after this. Therefore my red bull trick must be curing my colds.

For Monday

Read: Chapter 7 pages 216-223