CRITICAL THINKING – Fundamentals: Truth and Validity [HD]


(intro music) Hi! My name is Julianne Chung, and I am a graduate student
at Yale University. Today, I am going to talk
about truth and validity. There are many different good qualities that arguments can have. For example, they can be clear, they can be interesting, they can be persuasive, and so on. In this video, however,
we are going to discuss just two good qualities
that arguments can have that are particularly
important for determining whether we should accept
their conclusions. The first is this: the premises
of an argument may be true, that is, they may be in
agreement with the facts. In philosophy, truth and
falsity are held to be properties of statements,
but not arguments. Second, an argument may be valid. An argument is valid when its conclusion follows logically from its premises. In other words, an argument is valid just in case the truth of its premises guarantees the truth of its conclusion. In philosophy, validity and invalidity are held to be properties of arguments, but not statements. To see the difference
between these properties, it will be helpful to
look at some examples, all of which involve my good
friend Julia’s dog, Split. This is an example of an argument that has true premises and is valid. Premise (1): All Australian
Shepherds are dogs. Premise (2): Split is
an Australian Shepherd. Conclusion: Therefore, Split is a dog. In this argument, not only
are the premises true, but the conclusion follows
logically from them. Next is an example of an
argument that has true premises but is not valid. Premise (1): All dogs are animals. Premise (2): All cats are animals. Conclusion: Therefore, all cats are dogs. Here, the premises are obviously true, but the conclusion does not
follow logically from them. Of course, this argument
is clearly unacceptable, because its conclusion is obviously false. However, sometimes arguments
can have true premises, as well as true conclusions, but still be invalid
because the conclusions do not follow logically from them. Here is an example of such a case. Premise (1): All dogs are animals. Premise (2): All Australian
Shepherds are animals. Conclusion: Therefore, all
Australian Shepherds are dogs. Because of this, it is important that we are careful to ensure that the conclusion really does follow from the premises under consideration when we are evaluating an argument. We are now going to look at an argument with at least one false
premise that is valid. Premise (1): You can’t
teach an old dog new tricks. Premise (2): Split is an old dog. Conclusion: Therefore, you
can’t teach Split new tricks. Here, the first premise is false, but the reasoning is valid,
because the conclusion follows logically from the premises. Notice, too, that just
as in the last example, the conclusion of this
argument may happen to be true, although the argument does
not establish that it is. Alright, just one more example. This argument has at least one
false premise and is invalid. Premise (1): I like Split. Premise (2): Training dogs is easy. Conclusion: Therefore,
I’ll win a lot of awards for teaching Split how to roll over. In this example, not only
is premise two false, but the conclusion does
not follow logically from the premises. You’ve probably already
noticed that truth and falsity, as well as validity and invalidity, can appear in various
combinations in an argument, giving rise to four possibilities. Let’s take a moment to
review them together. Possibility one: we may
have our facts right, our premises are true, and
we may use them properly. Our reasoning is valid. Possibility two: we may
have our facts right, our premises are true, and
we may use them improperly. Our reasoning is invalid. Possibility three: we may have our facts wrong, some of our premises are false, and we may use them properly. Our reasoning is valid. And finally, possibility four: we may have our facts wrong, some of our premises are false, and we may use them improperly. Our reasoning is invalid. When we are evaluating an argument, we should only accept its conclusions if the first possibility obtains. Philosophers call such
arguments “sound arguments.” Because of this, you might be wondering why we should be at all interested in arguments that are valid,
but whose premises are false? One answer is that we are often not in a position to know whether
our premises are true. But being able to validly
infer the conclusions that would follow from such
premises if they were true sometimes enables us to
judge whether they are true. This is because validly
inferring a conclusion that we know to be false
from a given set of premises will tell us that one of our
premises must be false too. After all, a false
conclusion cannot validly be deduced from true premises. Consider the following example. Say that John calls his
boss at work one day, and tells her that he is in bed with a terrible case of the flu. His boss, it seems, could
use that information to construct the following argument. Premise (1): John is in bed
with a terrible case of the flu. Premise (2): If john is in bed with a terrible case of the flu, then he is not bowling. Conclusion: Therefore,
John is not bowling. This argument is valid. Its conclusion follows
logically from its premises. So, if John’s boss were
to see him bowling, what could she conclude? Premise (2) seems untouched
by this bit of evidence. Premise (1), however, is in danger. She could conclude that John is not in bed with a terrible case of the flu. It seems he lied. This is, of course, just
a very simple example. That said, hopefully it suffices to show that we often use reasoning like this to figure out whether
claims are true or false. Thus, it is indeed often
very useful for us to know whether an argument is valid, even if we don’t know whether
its premises are true. For more information about
truth, validity, and soundness, I highly recommend checking
out Paul’s video on validity and Aaron’s video on soundness. Subtitles by the Amara.org community

19 Replies to “CRITICAL THINKING – Fundamentals: Truth and Validity [HD]”

  1. The intellectual equivilent of tieing a shoelace. A sad sign of these dumbed-down times that it even needs to be "taught".

  2. I've been going through these videos in succession and so far the guy from Duke Uni. (Paul Henne) has given the best video. This one was convoluted and you went over your examples too fast, especially when involving the diagrams. A bit of a dry presentation.

  3. I should really keep up with these, do one a day. It's cognitively strenuous so it must be good for me. Also it's always good to maintain the fundamentals of thought. Going to add them to my watch later, which I tend to impulsively access from a browser shortcut.

  4. If it is stated in the Catholic Bible, the Catholic Catechism (which you can find online) or Ex Cathedra by the Pope, it is true, by definition. If not, it is either false or unimportant. If it contradicts any of those, it is false, by definition. It is required of us that we have the humility not to question this so that we might have a chance of entering Heaven, by Christ.

  5. Keep in mind that the arrangement of the final conclusion will affect if it is logic hence the validity. Try to watch the video few times. Always be logic. Hence, commonsense.

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