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There is a great divide in the world of rational argument: deductive and
inductive reasoning. All arguments fall into one camp or the other but what is
the dividing line? There's a lot of confusion out there about this. A quick
internet search will land you in a swamp of misleading or downright mistaken
descriptions. So let's make it clear right here at the start. What divides the
deductive from the inductive is intent. Deduction aims to provide certainty— it
offers a guarantee that the conclusion is true— proof with a capital P. Here's an
example: all foxes are canines. Some foxes sleep in trees. So some canines sleep in
trees. A closer look at this argument will show how deduction aims for a
guaranteed conclusion. Let's say all foxes in the world are in this circle. If
something is in this circle, it's a fox. Outside the circle—not a fox. And let's
say all the canines in the world are in this circle— wolves, coyotes, your
grandma's Yorkie— they're all in this circle. But anything outside this circle
is not a canine. Now the first premise says, "All foxes are canines." So you see
all these foxes over here outside the canine circle? No? Well, that's the point!
There aren't any. All foxes are canines, so if there are any foxes at all they
have to be right here. They couldn't be over here outside the fox circle—then
they wouldn't be foxes. They'd be some other canine like a jackal or a dingo. So
if it's true that all foxes are canines, then all the foxes in the world are
right here where the fox and the canine circles overlap. The second premise comes
along and tells us, "Some foxes sleep in trees." Let's say it's this one. So here's
our tree-sleeping fox— and as we've seen—right here in the overlap of circles is
the only place our tree sleeping fox can be, if it really is true that all foxes
are canines. So now the conclusion is proven: some
canines sleep in trees. It has to be true. After all, here's a tree-sleeping
creature inside the canine circle. Now that was a long, detailed look at a
deductive argument, and I don't want the main point to be lost. Can you see how
the conclusion is inescapable? Does your mind latch on to the conclusion with a
certain obviousness? That sense of certainty that you feel is exactly what a
deductive argument aims for. Let's go through one more deductive argument
quickly just to drive home the point. All unicorns always have a single horn. So
the next unicorn to magically appear will have a single horn. No surprise
there! After all we just said, "All unicorns
always have a single horn." So how could it have turned out any other way? If the
premise is true, then take it to the bank: so is the conclusion. Induction, on the
other hand, only tries to show that the conclusion is likely true— this is no
quest for certainty, just reasonable confidence. An inductive argument makes
the case that a conclusion is probably true. Look at this example. The last
unicorn to magically appear did not have a heart tattoo on its rump.
So probably the next unicorn to magically appear will not have a heart
tattoo on its rump. Now this is not a very strong argument. Who knows? Maybe
unicorns do tend to get hearts stamped on their flanks. But we haven't seen that.
In fact, the only unicorn we've seen so far did not have a heart stamped on its
flank. That's not great evidence, but it's some evidence. Oh! We got that one wrong.
But that's the nature of inductive reasoning. We're in the realm of
probability now— not certainty. And sometimes the conclusion of an inductive
argument turns out to be false, even when the argument is really strong. And this
one was never strong to begin with. We were reaching a tentative conclusion
based on a single piece of evidence. But let's change the example. What if a
unicorn magically appeared every single day for two weeks, and every single one
had a heart tattoo stamped on its rump. Would you bet your life that the next
unicorn will have a heart tattoo? Probably not. But can
you be reasonably confident? Sure! I mean, we've got a consistent two-week pattern
here! I'd wager 20 bucks or so that the next unicorn will have a heart tattoo on
its rump. But I might lose that 20 dollars. Inductive reasoning never provides
absolute proof— it's not even trying to. In this video I haven't even touched on
the many different styles and approaches of each camp, but when you're considering
an argument it's important to know which camp you're dealing with. Because you
can't decide whether an argument is successful unless you know what it's
trying to achieve. It would be unfair to call an inductive argument a failure
just because it doesn't provide absolute proof: absolute proof was never the goal.
So keep your eye out for the difference, and remember the difference is a matter
of intent.