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Types of arguments presented
in academic lectures, part 1. Well, you might be wondering why is
it important to know about different types of arguments. Well different types of arguments lead
to conclusions of varying strength. This is called the strength of inference. The strength can vary from necessary to easily falsifiable or easy to show false. They fall on a continuum. It's important to understand this
continuum in order to know when claims are reliable and
when claims are dubious or untrustworthy. So I have a task for you to try. Tell me how strong
are the following claims. Two plus two equals four. All bachelors are unmarried. There are 440 species of sharks. You have pneumonia,
a type of lung infection. Are any of these claims necessary claims? Let's come back to these later. Now I'd like to tell you about different types of arguments. The first type are deductive arguments. The conclusions to deductive arguments are necessary or in other words impossible to falsify. The second type are inductive arguments. The conclusions to inductive arguments are based on observation. And maybe falsified with new information. The third type are conductive arguments. The conclusions to conductive arguments are based on an analysis of independent reasons for and against a conclusion. You will encounter all three types
of these arguments in your studies. But there are some types that are more common in particular fields. I'll point those out to you as we go along. Let's talk about deductive arguments. Remember this two plus two equals four. Do you think that this is a necessary claim? Can two plus two ever not equals four? Well, this statement is necessarily true. And by mathematical necessity. We can also say that all even
numbers are divisible by 2. This means that when we
have an even number and divide it by the number 2,
there is no remainder. But can we trust that this is true
without testing every single even number? Is that even possible? No, but we know that the statement is true
by mathematical necessity nonetheless. What about this claim? All bachelors are unmarried. Can a bachelor be married? No, the statement is true and
always true by definition. Here's another one. Unicorns have horns. Well, of course they do. All unicorns have horns by definition. A unicorn without a horn would not
be a unicorn, it would be a horse. Let's take a look at classic
example of a deductive argument used in a intro to philosophy or
logic course. But first you must learn
what a premise is. A premise is a proposition or a sentence that serves to support
the conclusion of an argument. And the first premise of this
argument states all men are mortal. Mortal means not a god and
subject to death. Premise number 2 states,
Socrates is a man. The conclusion follows from
the premises by logical necessity and it states therefore, Socrates is mortal. When the conclusion follows
logically from the premises, the argument is called valid and
obviously this is a valid argument. When an argument is refered to as valid,
that means the structure of the argument is correct, whether or not any of
the premises or conclusions are true. Look at the structure of this argument. This is a valid deductive argument. What the letters represent and whether
they represent reality does not matter. If A=B and B=C,
then A=C by logical necessity. But one way to test a valid argument is
to see if when the premises are true, they lead to a true conclusion. Look at the premises in this argument. All men are mortal, and
all women are mortal. We know these premises are true. They reflect reality. However, is this argument valid if I conclude that therefore all men are women? No, you would laugh. That's ridiculous you would say. This is obviously an error in your logic. This argument cannot be valid. It is what we would call
an invalid argument. Okay. So, as I said, an argument does not have
to be true to be valid but when it is valid and also true, the argument
is called sound, a sound argument. So take a look at these premises again,
all men are mortal and all women are mortal. If I conclude, therefore,
all men and women are mortal. You would agree that this
argument is now valid. But also true. So it is a sound argument. Deductive arguments are used all the time. In your college courses, you will
encounter them in all your classes, but especially in mathematics,
statistics, engineering. And as I already mentioned,
philosophy and logic. In this video, you learned about three
kinds of necessity in deductive arguments. In the next video, I will be
discussing inductive arguments and conductive arguments. So make sure to watch part 2.

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