Lecture 2 – Fallacies of Relevance

Arguments that fail because of poor use of

inductive reasoning

During his interview with David Letterman, Kobe Bryant said the biggest problem facing the world today is the lack of education in inner-city schools, so it must be a very serious problem.

In his Logic 101 lecture last night, J.T. said that the Dallas Cowboys are a sure bet to win this year’s Super Bowl

Citing someone’s opinion as authoritative when said person is not an authority in the relevant subject areas

Expert opinions and testimony are great support for an argument- when said expert has any clue what they’re talking about

I.E. The Jenny McCarthy/Bono/Sean Penn fallacy

During his interview with David Letterman, Kobe Bryant said the biggest problem facing the NBA prospects today is overexposure to entertainment media. Since I’m planning on going pro in two years, I’ll remember not to pay too much attention to ESPN.

In his Logic 101 lecture last night, J.T. said that informal fallacies are tricky to accurately identify, so I’m going to be careful when I apply what I learned in class today.

Religion has existed since the dawn of human memory, but nobody has ever been able to prove that any supernatural being actually exists. Therefore, God doesn’t exist.

People have been trying to disprove and suppress religion since the dawn of human memory, but nobody has been able to completely silence the word of God. Therefore, God exists.

Trying to establish that P is true by citing that there is no proof for ~P (not P, or the negation of P)

An obvious problem is that it goes both ways, making the argument effectively useless As illustrated by the previous example

The key to this fallacy is knowing whether or not we can reasonably expect there to be proof It is entirely reasonable to suggest that we’ll never be

able to prove the existence of a god or gods

…but it’s reasonable to argue that if ESP was a real phenomenon, somebody would be able to prove it exists for all the attempts to make money off of it

Mort: Sorry, I can’t eat this pizza. It has pepperoni on it, and I don’t eat meat.

Nate: Why don’t you eat meat?

Mort: Because I’m Jewish, and God won’t be happy with me with I eat something non-Kosher.

Nate: Do you really think God cares if you eat pepperoni?

Mort: Prove to me that he doesn’t, and I’ll have a slice.

Similar to appeal to ignorance, but backwards.

The burden of proof is on the person making an unproven statement, not the other way around I can say that I was on Mars last night- you not knowing

where I was last night doesn’t prove I was on Mars.

Any legitimate claim can at least derive some logical foundation If a request for proof turns into “NO U”, you can

generally assume that they’re full of it and move along

If gay people are allowed to marry, it will legitimize alternative sexual relationships. Next, people will be arguing for polygamy to be legalized, then incest, then people will be trying to marry their dogs and horses! Clearly, legalizing gay marriage is a poor choice.

We have to stop the library from getting rid of pornographic books. Once they ban one form of book from the shelves, it won’t be long before they’re banning anything that creates controversy or bothers overprotective parents. The next thing you know, our public libraries will be censoring every word!

Establishing a chain of conditionals (If P, then Q) ending in an undesirable outcome. Since the end of the slope is bad, the first step in that direction must be bad

This fallacy depends on how strong the links between individual events are. Please explain to me how homosexuality and polygamy

are similar.

Keeping porn out of a public library is a pretty big step away from censorship

Your brake fluid lines are nearly cracked. If you don’t replace them soon, they will soon rupture, most likely when you are trying to stop (as this is when the fluid pressure is highest). This is very likely to result in a collision, which could seriously injure you and cost a lot of money. You don’t want this, so you should get your brake fluid lines replaced.

Oliver: Man, it’s hot today! The last time it was this hot out, my girlfriend broke up with me! I’d better not talk to that girl I have a crush on today.

Patty: The last time Republicans controlled the Senate, the deficit increased dramatically. High inflation is bad, so we better not elect any more Republicans.

Dr. Robert: In over 5 billions cases studied, it has been clearly demonstrated that, between the ages of 2 and 5 years, children’s vocabulary gets larger as their shoe size increases. Therefore, I would recommend stretching out your child’s feet if you want them to increase their vocabulary.

Attributing a causal relationship between two things when the only evidence is correlation or co-occurrence We can be pretty sure that Oliver didn’t get dumped

because it was too hot outside.

Correlation is not causation This doesn’t just apply to low sample sizes, as Dr. Robert

just demonstrated to us.

Stanley: All of the cars I drove growing up had automatic transmissions, and they also had good acceleration. So cars with automatic transmission must have better acceleration than cars with manual transmissions.

Tobias: I’ve driven on the freeways in San Diego probably 300 times, and I’ve never had traffic problems. It’s a good bet that San Diego doesn’t have very bad traffic.

Generalization is how all humankind learns things- if we waited for solid proof before being sure of anything, we’d probably never learn anything …case in point

However, you have to make sure your experience applies to what you’re generalizing If you drive on the freeway 300 times at 2 in the

morning, you’re not going hit traffic anywhere.

Quick generalizations aren’t necessarily bad, though.

When I put one of those berries in John’s coffee, he drank it and immediately started drooling and vomiting and twitching on the floor and then died. Those berries must be poisonous.

Walter: Giraffes and gorillas are to be found in Africa, and they both have names that start with ‘G’. Guinea pigs also have a name that starts with ‘G’, and so they are probably from Africa as well.

Analogies are great tools to expand our knowledge, but we must use them carefully.

When we have no reason to assume that things are related, we cannot use analogies to translate the nonexistent connection to something else