Non-Deductive Arguments

Here are the answers to the group work we did in class on args by example, args by analogy, args from authority, and args about causes. Conclusions are in bold.

1. That Honus Wagner baseball card shouldn’t be that valuable. After all, it’s made out of cardboard, and cardboard boxes at Pathmark are super cheap.

Analogy
Bad - Material isn't always a relevant similarity to draw a conclusion about value: baseball cards are typically valued for their rarity, not what they're made of.

2. China, India, Brazil, Nigeria, and Russia are all countries with populations greater than 100 million citizens. Hence, most countries have populations larger than 100 million citizens.

Example
Bad - 5 countries out of about 200 total nations is too small a sample. Also, the examples are cherry-picked, and so they're unrepresentative.

3. In a recent study, 100% of those who took a new birth control pill didn’t get pregnant. Only males participated in the study. Thus, the birth control pill must be very effective.

Cause
Bad - A better explanation of the correlation between taking the pill and not getting pregnant is that males don't get pregnant.

4. Oasis sounds just like The Beatles. We all know that The Beatles were one of the most influential rock bands ever. So Oasis must be one of the most influential bands, too.

Analogy
Bad - A similar sound isn't a relevant enough similarity regarding whether a band is influential.

5. Abortion is morally acceptable because renowned linguist Noam Chomsky has defended the practice of abortion, and he’s pretty smart.

Authority
Bad - Chomsky's expertise (linguistics) isn't relevant to the topic of abortion.
(Chomsky explains his view on abortion in the video to the right.)

6. Most people say the money it costs to go to law school is worth it, because lawyers earn a lot of money. So, since doctors also earn a lot, med school costs must be worth it, too.

Analogy
Pretty Good - The similarity (average money earned per profession) is relevant to whether med school is financially worth it. Assuming one thinks a large up-front investment is worth an even larger salary in the future, this arg is good.

7. My friend knows me better than anyone else, and he says I’m a decent guy. Therefore, I must be a decent guy.

Authority
Bad - Yes, my friend is a relevant expert, but he's likely to be biased in favor of me since he is my friend.

8. My sis usually keeps her car windows rolled down, though she always rolls them up right before it rains. Her car must be magical, then: rolling up her windows causes it to rain.

Cause
Bad - This is reversed! The rain probably causes her to roll up her window, not the other way around.

9. I expect this new pair of cheap, black shoes to last me about 9 months, since the last pair of cheap, black shoes I bought wound up lasting about 9 months until I wore them out.

Analogy
Pretty Good - More information would be better--for instance, it's not clear whether the two pairs of shoes are the same brand and model--but the similarities (same owner, cheapness) are relevant to the conclusion of how long the shoes will last.

10. In 2006, Philadelphia had the highest murder rate in its history. That same year, Mark Wahlberg spent a lot of time in Philadelphia while filming the movie Invincible. Thus, Mark Wahlberg’s presence in Philly probably led to such a high murder rate.

Cause
Bad - This is most likely a coincidental correlation between Wahlberg's stay in town and the high murder rate.