Today, we're going to talk about 
fallacies, of relevance. 
Lets start, by talking about ad hominem 
arguments. 
Ad hominem means to the person. 
An ad hominem argument is an argument 
that starts with premises about a 
particular person, a person who is 
engaged in making some point or defending 
some claim. 
And then, it draws a conclusion from 
those premesis against the point that the 
person was making, the conclusion that 
they were attempting to defend. 
So, I can try to make this idea clearer 
by giving three kinds of examples of ad 
hominem arguments. 
The three kind of examples that I'm going 
to be talking about today are deniers, 
silencers, and dismissers. 
Let's consider an example from each kind. 
[SOUND] 
So, 
a denier ad hominem argument is an 
argument that begins with premises about 
a person who is making a certain point or 
defending a certain claim and concludes 
that a point that they were making or a 
claim that they were defending is false. 
Let me give you an example of a denier ad 
hominem argument. 
Suppose that Lucy has been accused of 
murder. And her alibi is that, at the 
time the murder was committed, she was 
with Louie. 
Now, Louie gets up and testifies that he 
was with Lucy at the time the murder was 
committed and she was nowhere near the 
scene of the murder. 
But now, suppose we find out that Louie 
has a history of perjuring himself on the 
stand. 
He's paid to purger himself. 
He's a very good perjurer because he can 
pass lie detector tests with flying 
colors even when he's lying. 
And he doesn't exhibit any of the 
behavioral signs of lying that's 
detectable by the police or any other 
courtroom expert. 
So, Louis makes a living as a hired 
perjurer. 
That's something we find out about Louie. 
Now, if we find this out about Louie, 
that could lead us to conclude that what 
Louie said on the stand was false. 
He was purjuring himself, as he normally 
does. 
So, here we have an ad hominem argument. 
We start with premises about Louie, that 
he's a hired perjurer, that he perjures 
himself regularly in the courtroom when 
he's on the stand. 
And, we draw a conclusion about the truth 
of what it was that Louie said on this 
occasion, namely that it's false that he 
was with Lucy at the time of the murder 
was committed. 
That's an example of a denier ad hominem 
argument. 
Now notice, the particular argument I 
just gave seems like a pretty good 
argument. 
In fact, this is a case of an ad hominem 
argument that is not fallacious. 
It doesn't commit a fallacy of relevance. 
If, in fact, we do find out that Louie is 
a hired perjurer, that he's a career 
perjurer, then we should conclude that 
what he's saying on the stand, in this 
instance, is false. 
That's at least pretty good evidence that 
it's false. 
So, this is a case where we have an ad 
hominem argument that's not guilty of a 
fallacy of relevance. 
But consider another case where we have 
an ad hominem argument that's a denier 
but that is guilty of a fallacy of 
relevance. 
Suppose that Louie is not a career 
purgerer at all. 
Louie gets on the stand and testifies 
that he was with Lucy at the time that 
the murder was committed. 
But, Louie is dressed in really, really 
shabby clothing that he probably bought 
in the 1970s. 
Under these circumstances, we might 
conclude that what he's saying is false. 
But why would we conclude that? Well, we 
might say, 
look, the guy dresses in really shabby 
clothing that he bought in the 1970s. 
He's got to be lying. 
Now, that's an ad hominem argument also. 
It starts with premises about the person 
who is testifying, in this case Louie, 
and it draws a conclusion about the truth 
of his testimony. 
In this case, that what he was saying was 
false. 
But that ad hominem argument, though it 
is a denier like the first ad hominem 
argument that we considered, is a 
fallacious argument. 
It's not a good argument at all. 
Just because Louie is dressed in shabby 
clothing that he bought in the 1970s, 
that has no tendency whatsoever to show 
that what he's saying was false. 
So, deniers are a kind of ad hominem 
argument. 
But, some of them commit the fallacy of 
relevance and some of them do not. 
Now, let's consider another kind of ad 
hominem argument. 
The second kind of ad hominem argument 
I'm going to call a silencer. 
[SOUND] The second kind of ad hominem 
argument that I want to discuss is the 
kind of argument that we're going to call 
a silencer. 
A silencer is an argument that starts 
from premises about a person who is 
trying to make a point or defend a 
conclusion, and that person's entitlement 
to make that point or defend that 
conclusion in the situation which they 
were doing so. 
It starts from premises about that and 
moves to a conclusion about the point 
that they were making, or the conclusion 
that they were defending. 
So, let me give you an example. 
Suppose that while Lucy is on trial for 
murder, and witnesses are being called to 
the stand, lawyers are questioning them 
and cross examining them. 
All of a sudden, Charlie runs into the 
courtroom, breaks open the door and yells 
at the top of his lungs, I saw Lucy kill 
the victim. 
Okay. 
Now, Charlie might say that. 
But in that situation, in the middle of a 
courtroom, that is not something that we 
can take into account in determining 
whether Lucy is innocent or guilty. 
The jury cannot consider Charlie's 
testimony, if that's what you want to 
call it. 
That testimony does not count as evidence 
in a courtroom. 
So, we could say Charlie had no right to 
say what he did in the situation in which 
he said it. 
He was not entitled to speak in that 
context. 
So, his testimony is invalid. 
Discard it, don't pay any attention to 
it. 
That's an example of, a silencer 
argument. 
It's an argument that starts from 
premises, about Charlie's entitlement to 
speak in that situation, and moves to a 
conclusion about whether we should pay 
attention to what he was saying. 
That's an example of a silencer argument. 
But that silencer argument is a justified 
one. 
It's not fallacious. 
Here's an example of a fallacious 
silencer argument. 
Suppose that Charlie is called to the 
witness stand and he's examined by one 
lawyer and cross examined by another 
lawyer. 
And during the course of his testimony, 
Charlie testifies that he did see Lucy 
murder the victim. 
He saw with his own eyes. 
But, as he's testifying, 
he speaks in an unusual foreign accent. 
Now, someone might say, well, Charlie 
speaks with an unusual foreign accent, 
therefore, we should pay no attention to 
his testimony. 
Now, that's also a silencer at hominem 
argument. 
But that's an example of an unjustified 
silencer ad hominem argument. 
Just because Charlie speaks in an unusual 
foreign accent, that's no good reason to 
think that we shouldn't pay attention to 
his testimony. 
So, there's a case of an ad hominem 
silencer that does commit a fallacy of 
relevance. 
The third kind of ad hominem argument 
that I want to talk about is a kind of 
argument that we're going to call a 
dismisser. 
[SOUND] A dismisser is an argument that 
starts from premises about a particular 
person who's trying to defend a 
conclusion or make a point. 
And the dismisser argument moves from 
those premesis to a conclusion that says 
that we have no reason to believe the 
conclusion the person is trying to defend 
or the point they are trying to make. 
The dismisser argument doesn't conclude 
that we should not believe what the 
person is trying to defend or the point 
they're trying to make. 
Rather it concludes that we have no 
reason to believe, the conclusion the 
person is trying to defend, or the point 
they're trying to make. 
Rather it concludes that we have no 
reason to believe the conclusion of the 
person that's trying to defend or the 
point they're trying to make. 
Now, what's an example of the dismisser 
argument? Well again, consider the 
situation where Lucy is on trial for 
murder. And now, Linus is called as a 
witness. 
So, lawyers are questioning Linus and 
Linus says that he saw Lucy kill the 
victim with her Acme double-edged knife. 
And then, Linus throws in, for good 
effect, acme, there's no knife like it. 
Now, as Linus offers this testimony, he 
happens also to be wearing his Acme 
promotional t-shirt, his Acme baseball 
cap and carrying a big briefcase that 
says acme on it. 
The cross examining lawyer finds out that 
Linus is actually a sales representative 
for the Acme Double-edged Knife Company. 
Now, under these circumstances, we might 
wonder whether Linus isn't just saying 
that he saw Lucy kill the victim with her 
Acme double-edged knife in order to 
promote Acme knives as effective knives, 
as useful tools. 
Now, if that's why Linus is offering his 
testimony, then, we should think of his 
testimony as a form of advertising. 
Not as something that gives us a reason 
to believe that Lucy actually did kill 
the victim with her Acme double-edged 
knife. 
Linus has an interest In getting us to 
believe that Lucy killed the victim with 
her Acme double-edged knife. 
But his interest in getting us to believe 
that is not just an interest in getting 
us to believe the truth, it's an interest 
in making some money for the company he 
represents. 
So, that leads us to wonder whether 
Linus's testimony is trustworthy. 
So we can say, Linus is a representative 
for the Acme Double-Edged Knife Company, 
therefore, his testimony to the effect 
that Lucy used an Acme double-edged knife 
to murder the victim is not testimony 
that we should trust. 
Because he has a vested interest in 
offering that testimony. 
There's a case of a dismisser ad hominem 
argument. 
But that dismisser argument may be 
justified. 
We could give another example, though, of 
a dismisser argument that is clearly 
unjustified but commits a fallacy of 
relevance. 
An example like that would be the 
following. 
While Linus is saying testifying in the 
courtroom that Lucy killed the murder 
victim with her Acme double-edged knife. 
Linus actually doesn't work as a sales 
representative for the Acme Company not 
does he have any interest in promoting 
Acme double-eded knives. 
But Linus might look like someone who 
used to work for the Acme Double-edged 
Knife Company. 
and because of that resemblance, we might 
be led to think that Linus is as much of 
a salesman for the Acme Double-edged 
Knife Company as this other person was. 
They look like each other, maybe Linus 
reminds us of him. 
And so, we might be led to think, based 
on the resemblance between Linus and this 
Acme double-edged knife salesman, that 
Linus himself has a vested interest in 
promoting Acme double-edged knives, and 
so would be willing to offer false 
testimony in order to have a product 
placement opportunity for Acme 
double-edged knives. 
Now, that would be an example of a 
dismisser ad hominem argument that is 
fallacious. 
It draws a conclusion based not on any 
good reason for that conclusion, 
bu rather, based on some resemblance 
between Linus and somebody else. 
A resemblance which is presumably 
irrelevant to the truth of what Linus is 
saying. 
And so, our argument would in that case 
be fallacious. 
It would be a fallacy of relevance.