[Intro Music]
Hey there, students! If you clicked on this
video, I assume that you want to know the
difference between deductive and inductive
reasoning - so let me tell you.
Now, first of all, deductive reasoning has been around
a lot longer - goes all the way back to Aristotle.
Deductive reasoning is a method of reasoning
by which you start with a premise and you
go to another premise and these premises lead
you to a conclusion. If you've done this right
and logically and all that, then you have
arrived at something that is certain. A certain
conclusion, meaning not just a certain conclusion
but a conclusion that we can be certain of.
Then, there is inductive reasoning. And inductive
reasoning - fast forward about 2,000 years
- and we go to Sir Francis Bacon, a 17th century
English natural philosopher (which is what
they called scientists back in the day). And
inductive reasoning - instead of starting
with a general premise and moving on to a
particular premise and then getting to an
answer that way - Sir Francis Bacon said that
the way we arrive at truth is to make repeated
observations and then out of those observations,
we generalize these repeatedly observed phenomena
into a probable conclusion. That's the very
simple version. Now, he outlined this in his
Novum Organum in 1620, which means New Method.
Now, keep in mind, new method as in a new
method - the old method's been around for
like 2,000 years. So what you have to keep
in mind here is when Bacon is bringing forward
this inductive reasoning that he is challenging
Aristotle, which is something that's really
kind of distinctive about the Scientific Revolution
is this willingness to challenge ancient authorities
- that people had not done for about 2,000
years when you think about these ancient authorities
like Aristotle... that they were still towering
very high. And Aristotle is still a big deal
today but he's certainly not the foundation
for physical science or anything like that.
The simplest way that we can compare inductive
and deductive reasoning is to look at deductive
reasoning as "top down," where we start with
a generalization and it leads us to a specific
instance - that the conclusion is very specific.
Whereas inductive reasoning is bottom up...
[Laughs] You said bottom!
Where we start with a number of specific instances
and that leads us to make a generalization.
Now, of course, as in anything philosophical
or scientific - that many experts will say
that this is an oversimplification but, at
the same time, it does help.
By the way, shout out to Dr. Karl Carpenter
- my first principal and the first guy ever
to talk to me about inductive and deductive
reasoning.
And so, with deductive reasoning, conclusions
are drawn from premises. You start with premises.
Top down logic again.
Now, as far as these premises, the most classic
example of a premise is when Aristotle says,
first of all, "All men are mortal." We start
with a general premise and then we look at
a specific situation. "Socrates is a man;
therefore, Socrates is mortal." Going from general to specific.
I've got a video on Rene Descartes, who was
a philosopher of the Scientific Revolution.
And Descartes is most famous for saying, "Cogito
ergo sum." I think, therefore I am. Now, Cogito
ergo sum is actually a statement of deductive
reasoning because what Descartes did is he
came to the conclusion... He's trying to figure
out if he exists. Alright, this guy, he went
REAL deep.
Descartes says, first of all, "What thinks
must exist." Alright? That something that
thinks can only do that if they exist. Two,
"I am thinking." Therefore - or, in Latin,
ergo - "I exist." I think, therefore I am.
Deductive reasoning.
Then, we bring in our friend, Blake - 10th
place at the National FFA Convention. We're
really proud of that guy. Now, starting with
premises, first of all, "Good students pass
exams."
Second, "Blake is a good student."
Third, "Blake will pass his exam."
Blake better pass his exam! Alright? But if
Blake does not pass his exam, then what I
would need to do is I would have to go back
and check my premises - that at least one
of those premises must be wrong if the conclusion
is false. Either 1) Blake is not a good student
or 2) maybe not every good student passes
exams. So, maybe I came to a false conclusion.
So this is one of those things that the conclusion
can kind of stand until you realize, "Wait...
That's false." And then I go back to the premises
and I figure out which one was false and if
my logic didn't add up or something like that.
Deductive reasoning.
[Music]
So as far as inductive reasoning, we draw
conclusions from observations. So we start
with observations. This is what we call (in
science and philosophy) empiricism, which
was a big deal during the Scientific Revolution
and the Enlightenment. And this is really
about connecting the dots and the more data
we have, the greater the probability of the
conclusion being true. So for example, if
we were to look at these three dots, what
do you see?
Dramatic Pause!
Did you see... a triangle? Well, it could
be a triangle, but then again, it could also
be... a circle.
See? Three points on a circle. Three points
on a triangle. Don't you feel stupid now if
you saw the triangle? Well, actually, the
thing is though, we don't know what it is.
It could be a triangle. So the thing is, when
we get more data, then this is looking more
like a triangle. Then again, it could be something
else. But we see that, "Okay, a triangle fits
here and a circle does not fit here." So we
know that that is not a circle. So the more
data, the closer we are to certainty, although
we don't quite get there, which is what David
Hume, the "Skeptical Scotsman," has to say
about the problem of induction. That really,
when it comes down to it, induction cannot
ever lead us to certain knowledge because
it presupposes that things will stay the way
they always have been. So, for example, if
I were to say, "The sun always rises in the
East," what I'm really saying is there is
a very high probability that the sun will
rise in the East - that it always does - because
we have always seen it that way. But are we
certain that the sun will rise in the East
tomorrow? Okay, think about your ex-boyfriend
or ex-girlfriend or something like that and
it's like, "This person loves me..." Well,
you know you believe that because that's been
true but is it always true? Does it remain
true? Usually, it does not. The one constant
we can count on is change.
Another thing that's used often is when someone
says that all swans are white. What you're
really saying is that, "All swans that I've
seen are white" and not all swans because
I have not seen all swans and therefore, I
can't make that judgment.
Now, keep in mind that certainty is not even
the goal of inductive reasoning because while
deductive reasoning aims to arrive at certainty,
inductive reasoning is only a function of
probability and saying that we can infer that
this is true - that there is a high probability
that this is true - not that we can ever be
100% certain of anything because science changes.
It evolves over time. You know, we don't base
our physics on Aristotle anymore.
So when it comes down to it, the Scientific
Method is a repeated process of induction
and deduction. It's not that one of these
reasoning forms is better than the other...
They're different.
So, that's about it! Hopefully, you learned
something and if you did, please subscribe.
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I'll be back soon with some more lectures
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other good stuff.
Until next time... {snaps]
[music]
