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Logical Fallacies

Chris Lele
Lesson by Chris Lele
Magoosh Expert
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Okay, in this video, we are going to meet the logical fallacies. We're gonna first talk about what the logical fallacies are exactly. And then we're gonna meet them in terms of examples. So first off, logical fallacies. There is actually formal logic here that deals with logical fallacies. And informal logic, names, Latin names, scary sounding Latin names are given to different types of logical fallacies.

The great news for us here as revised GRE students, on the AWA we do not need to know that, whatsoever, we simply need to note that the argument is not valid for a certain reason. However, we decide to phrase that is the key because the jury's not testing our ability to know Latin words for logical fallacies but really they're testing the way we think.

They wanna know, can we identify the holes in this argument? So, that said, here when I go and give my examples of logical fallacies, I just given them my own days, so we can put them in categories so we know what to look for. So first off, we have the things change fallacy and get it doesn't sound very formal at all. Of course it's not the point.

So what is the things change fallacy? So here's an example. It says, in 85, Hamson, a leading player in the aftershave market, launched a successful ad campaign. Therefore, Hamson, if it wants to repeat this success, should launch the same ad campaign.

Well, hold on, things changed, what worked in 1985 isn't necessarily gonna work today. Why? Well, maybe the people, their customer-based has changed. So if an ad campaign targeted older men and had maybe images of yachts or whatever it is old men like, it wouldn't work if now Hamson targets a younger demographic.

So there could be all these reasons why this argument doesn't hold true, but as soon as you see this, you go, okay, well, things change. So base my attack of the argument on that. And then of course you wanna come up with reasons why things changed. How did things change? And of course, I gave you an example just now, the demographic.

So that's what we're gonna do here on most of these examples. I'm gonna basically tell you the name of it, how it pertains to this argument or how it pertains to this example, and then of course how we could come up with alternate explanations to improve the argument. Okay, let's try it with number 2, assumed cause and effect. What's the assumed cause and effect, let's have a look.

After instituting a comprehensive bilingual education program, Monte High witnessed the greatest percent of its senior class go on to college. Therefore, Monte High should continue the bilingual education program. Well, wait a second, just because it was bilingual education program doesn't mean suddenly that, that's why people were accepted to colleges as though colleges were basing their mission solely on whether or not these students are taken in by program.

Now, the key here, though, again, is improving the argument. What else could account for this? Well, a host of other factors. Maybe new teaching staff. Maybe there was some other form of curriculum. Maybe they had, say, coaches on hand.

Maybe they had a superstar SAT teacher. All of these reasons could work or account for the fact that more Monte High seniors than ever before went on to attend college so we can't just assume it was this bilingual education program. Okay, so those are two, now we have a few more to go. So let's take a look at the next one.

Numbers and percentage assumptions. What's going on here? Let's say more students. Here you go, Monte High again, more students for this year senior class of Monte High went on to college. Therefore, the seniors are Monte High's most successful.

So you have more, you have a number here. What does this number mean? Well, imagine this. Imagine, let's just make it the 2010 class here, Monte High. The 2010 class, you had 100 students. And 99 went on to attend college.

That's amazing, wow. And then, this year 2011, the year we're talking about here, we had 200 students in the class. They combined, maybe, with another school. And out of the 200, 100 went on to college, which is more than 99. But wait a second, is that necessarily better?

So percentage wise, 99% went on to attend college and only 50%. So you have to be able to account for these numbers, and sometimes I call these math assumptions. So think of it in math terms. Now, for the next one, we have vague language. What do we have here?

Studies have shown that those who eat three maxomeal fruit bars a day are in better shape than those who eat a normal diet. Okay, wait a second. What do we mean in better shape? How do you quantify that? How do you come up with this?

So this is very vague than those who eat a normal diet. Is there is anything wrong with that? What do we mean by a normal diet? Again, this is very vague so we need to be able to pick up on those terms and say, what does it mean to be a better shape and then delve into that, show how that can be hold the argument because when they may say a better shape means that they run more.

Well, how's that better shape? So of course try to take apart the argument based on these things, don't just say, the language is vague, end of story. No, the language is vague. What must the argument do to make this language less vague or give us something specific it quantify better shape.

Okay, well, they lost 10 pounds versus they a normal diet, normal diet being what? Again, define terms. Make sure this has to be specific as possible in order for the argument to be more valid. Okay, there are a few more to go, as I said.

And next one, we have not all X are alike, so X being a certain group. So a recent study found that 50-65 year old in Gambitville responded favorably to a new anti-cholesterol drug. Therefore 50-65 year old males in Smugburg will also respond favorably to their drug. Okay, so it is assuming what that the 50 to 65 year olds in Gambitville are the same as the 50 to 65 year olds in Smugburg.

Now obviously there's gonna be significant overlap. They're both males, same group. However, there can also be subtle differences. So what would be some subtle differences or maybe they're not even that subtle, maybe Gambitville is in a part of the country, whether they're fond of very rich heavy foods.

And Smugburg is maybe more similar to where I live in California where people are very much into eating healthy and fitness, we don't know but you can't compare one group to another group in a different country. They're not alike, or different city. In this case, they're not alike in all cases, so of course you wanna come up with some alternative explanations.

Okay, so next one is don't trust a survey. And this one's pretty typical, you can kinda see this one coming from a mile away. So it usually says according to some sorta surveys. So according to latest survey, the residents of Monroe Town are unlikely to commute to neighboring Jacksonburg unless a new highway's constructed.

Therefore, the highway should be constructed. Well, okay, so it's assuming that just because the survey said something that we can really trust the results. So did it pull all the residents from the town? Maybe just specific ones. And even if it pulled all the residents just because these residents say something.

That, yeah, we're gonna start commuting if this highway is constructed doesn't mean they are actually going to start commuting once the highway is constructed. Again, that's what you wanna look for them. Finally, we have here, apples aren't oranges. I call this the different cities. You'll see why in a minute.

But the idea is that you assume two things are alike, but they're not because apples aren't oranges. What do we have here? We have, since building a subway system Gap Town has been able to cut down on its citizens' average commute. Therefore, Percyville should also build a subway if it wants to reduce the average commute for its citizens.

Okay, so what's going on here? Well, we're assuming that what works for Gap Town, the subway system right here, is gonna work for Percyville. So, therefore, cuz it worked in Gap Town, it should work in Percyville, this subway system. But wait a second.

How do we know that's the case? Maybe Percyville and Gap Town are very different. Very different or not a lot. Do not not equal one another but of course you can't just stop there. You have to say what? Maybe Percyville most have to commute long distances, maybe there is no central downtown and therefore building a subway system isn't gonna do much good.

So you can maybe go into depth about traffic patterns, any other possible explanations, that's what we're going for here. Once you identify in your own words, please don't put out, this is an apples to orange fallacy. You wanna simply say the argument assumes that Gap Town is the same as Percyville. However, these two cities can differ for many reasons.

First off, Percyville could be dot dot dot. That is how you wanna attack these logical fallacies.

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