Common Logical Fallacies | Rhetoric


In this video I’d like to address some
common logical fallacies. By the word “fallacy” we mean a mistake. So these are
mistakes in reasoning. And there are quite a few of them, but we’re just going to restrict ourselves to some of the more common ones. The first example here reads, “Professor Karl Knutson has recently
argued that all coffee drinking in public places should be banned.
Knutson believes that coffee is an addiction and that all addictions are
evil.” What we have here is in some ways a strawman argument … and the idea is that if you summarize an opposing view in such a way that it’s not a fair summation, that it’s more of a caricature, then you’re guilty
of using a strawman argument. And you can see here that by saying
that Knutson believes that all addictions are evil — these are very
strong words. They’re very general. Maybe Knutson doesn’t believe his position
quite that strongly. So in that case we are guilty of using a strawman argument.
The second one reads, “It is Knutson who is evil. Did you know that he divorced
his wife just because of her coffee breath?” In this case what we have is
what’s called an ad hominem argument … ad hominem … and you’ll see that a lot of
these mistakes have Latin names. This one here literally in Latin it means “to
the man.” This mistake is where you attack the person as opposed to the
issue or the view. Sometimes that may be legitimate, for instance if you’re in a
courtroom and you’re trying to discredit a witness. But most often in public
discourse that’s not appropriate, and you should really try to stick to the issue.
The third one reads, “But then it’s typical of a Swede to think only in
absolutes,” and so on. Now this one is an example of stereotyping … where we generalize about a particular group of people or a particular issue.
I don’t think I have to explain too much about what this is, but it is
something to watch out for. Number four reads, “If you love coffee, however, then you’ll agree with me that Knutson should be
roasted for his views.” This is what we might call a non sequitur … another Latin title. Literally this means “it does not follow.”
It’s also the title of a comic strip by the way which is quite funny. So the idea
here is that if we have A and we say it leads to B, but the logic is not quite
there, then we’re dealing with a non sequitur, something that does not follow
from something that came before. Number 5 reads, “Either coffee is an
addiction or it is the most liberating beverage on earth.” And here we have
what’s called an either-or fallacy. Either it’s this or it is that. We tend to do this more often, where we just give two
alternatives or two options where there may actually be more, and we shouldn’t
restrict ourselves too much. Number 6 reads, “After I turned 18 and began
drinking 6 cups a day (in my teen teenage years I limited myself to 4),
my productivity soared,” and so on. This is called a post hoc argument. Post hoc is short for a longer Latin phrase which goes “post hoc
ergo (ergo means therefore) propter hoc,” and “propter” means “because” and “hoc” means “this.” So literally this means “after this therefore because of this.” Sounds
very complicated, but it’s actually fairly straightforward. If you have
event A and you have B, and B happened some time after event A then you might
suppose that A has caused B, but that’s not necessarily the case. Just
because one thing happens after another doesn’t mean that A has caused B. So that’s a post hoc fallacy. Then we have 7, which reads, “So
join me in the fight for public coffee consumption. If we don’t fight for the
right to drink an espresso or cappuccino we may soon lose our
privileges.” This is a slippery slope argument. The idea is
fairly simple. Think of a slope and if you start with something, if you give in,
and, you know, you say “well this is okay” then the ball starts rolling and
you end up further down the slope. So slippery slope arguments may
have some validity sometimes, but on the whole you should watch out for them. And then the last one here reads, “Fortunately Knutson hasn’t reckoned with the fact
that many of us are willing to make a stand. If enough people speak up then
Knutson will know once and for all that he is in the wrong.” This last one
here is a bandwagon appeal. The idea is that if you jump on
the bandwagon, if you join popular opinion, then you may think you’re right,
but it’s not necessarily the case that the majority of the people (or many
people who are fashionable and popular) are necessarily correct. Okay, so those
are some of the most common fallacies we have in logic and in rhetoric, and those
are ones definitely to watch out for.

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