03a. How to Argue - Induction & Abduction. Part 1/2.
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Why do you really want to see the new Marvel movie, even though you haven't heard anything about it, good or bad? Your ability to do things like predict how a medication will affect you, or what movie you might like, or even things like what the perfect gift might be for your best friend, or what's the fastest way to get to campus –- all of this stuff, you know through induction.
Deductive arguments are great because they give us certain answers.
But unfortunately, much of the world cannot be summed up in a neat deductive proof. Deduction requires a fair amount of general information to give you a specific conclusion that is, frankly, probably kind of obvious. So, philosophy -- and basically, you know, life as well -- require that you have other ways of reasoning.
In addition to knowing how one fact leads to another, you also need to take what you've experienced before, and use that to predict what might happen in the future. And you need to be able to rule out what can't be true, so you can focus on what can. Through these kinds of reasoning, you're not only able to figure out stuff like how to fix your headache, and why your roommate might be acting weird.
You can also come up with better, more skillful arguments — and counterarguments — which are some of the most important maneuvers in the philosophical game. And maybe the best part is, you already know how to use these techniques. In fact, I bet you've used them this very day.
You know this! [Theme Music]
If you possess any ability to really predict the future, it lies in your ability to reason inductively.
Inductive reasoning relies on the predictability of nature to reveal that the future is likely to resemble the past, often in important ways. For example, there's tons of research to support the knowledge that aspirin – acetylsalicylic acid -- is an effective treatment for pain, like headaches.
And you probably have personal experience with the effects of aspirin, too. So, you believe that this aspirin tablet will cure the headache you have right now, because countless aspirin tablets have cured countless headaches in the past.
Likewise, you want to see the new Marvel movie, because you liked most of the other ones, so you believe that they'll continue to deliver for you, entertainment-wise.
But it's important to remember that, unlike deduction, where true premises entail true conclusions, inductive premises only mean that the conclusion is likely to be true.
Inductive arguments don't provide you with certainty.
Instead, they work in terms of probabilities. And they're useful for more than predicting what's going to happen. For example: Most men in ancient Athens had beards.
Socrates was a man who lived in ancient Athens.
Therefore, Socrates probably had a beard.
This is an inductive argument, because it starts with what we already know – about the grooming habits of ancient Athenian men, and about the time and place in which Socrates lived – and makes an educated guess based on that information.
There's no guarantee that the conclusion is correct, but what's known would seem to support it.
Reasoning like this is incredibly useful, which is why it's so common. But there's also a problem. The future doesn't always resemble the past. And every pattern has its outliers. So induction always has the potential to produce false results. Aspirin might not work on a really bad headache. The new Marvel movie might be awful. And, yeah, maybe a specific guy in Athens had a beard but it's possible he didn't! While the world tends to work according to predictable rules, sometimes those rules are violated.
And you know what you need when that happens? A little Flash Philosophy. Off to the Thought Bubble. Contemporary American philosopher Nelson Goodman confronts the problems of induction, using a thought exercise about a hypothetical substance called grue.
According to Goodman's scenario, grue is anything that's the color green before a certain time, a time that we will call t. And another property of grue is that, while it's green before time t, it's blue after it.
Now, let's assume that we're living in a time before t. t could happen a hundred years from now or tomorrow, but we know that all of the emeralds we've ever seen are green.
So, inductive reasoning lets us conclude that all emeralds are green, and will remain green after time t -- since emeralds haven't been known to change color.
BUT! All emeralds are grue! Because it's not yet time t, and they're green, which is part of the definition of grue. So we have no choice but to conclude that the emeralds will be blue after time t arrives.
Now we've got a problem. Because inductive reasoning has led us to conclude that emeralds will be blue after time t, but inductive reasoning also tells us that they'll remain green. Goodman's riddle reminds us that inductive evidence can be flawed, or contradictory.
It can make you think that you can predict the future, when of course you can't. So, there are times when you need to get at the truth in other ways.
Like by eliminating what's obviously not true, and considering what's most likely. And for this, we turn our attention to one of the most important philosophical figures of 19th century England: Sherlock Holmes.
In chapter six of Sir Arthur Conan Doyle's “The Sign of the Four,” Mr. Holmes says, and I quote: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”
This is probably the best, most succinct description ever given of the kind of reasoning known as abduction.
Which I know, it sounds like we're talking about a kidnapping or something, but abduction is a thought process sometimes described as “inference to the best explanation.”
