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| Proof and Evidence
How do you know when something is true?
How do you know whether the sun will rise tomorrow? How do you know that you are not dreaming now? How do you know that your teacher has not been possessed by aliens? And how would you know if he had? In fact, how do you know that anything is true? Knowing how to tell if something is true is a problem that humans have worried about for thousands of years. It matters in every aspect of what we do. Juries, for example, have to decide whether a defendant is telling the truth when he or she says, "I didn't do it." Scientists have to decide whether new scientific theories are true. Kids have to decide whether Sony is telling the truth when the company claims that PlayStation is better than Nintendo 64. Some of these claims are easier to prove true (or false) than others. Some very clever people have come up with categories to help us figure out how we know something is true and how certain we can be that it is true. You're going to learn about those categories right now.
Really knowing something is true: logical proof
The best, most convincing kind of argument that something is true is called a logical proof. When something is logically proven, it means that the true answer is the only one that really makes sense. For example, suppose I told you that all Martians are purple and that my friend Quatto is a Martian. What color is Quatto? Of course, you know that Quatto is purple because you know that all Martians are purple. Assuming that the first two statements are right—that all Martians are purple and that Quatto is a Martian—then logically, Quatto has to be purple. This kind of argument, which is known as deduction, is just about the strongest kind of proof there is that something is true. Unfortunately, most things are really hard to prove true by deduction.
Assignment #1:
There is a very wise robot named Mr. Mind who lives on the Internet. Mr. Mind does not believe that you are human; he thinks you're a robot like him who is only pretending to be human. Go talk to him and prove to him that you are, indeed, human. Then send me an email telling me what you learned from your conversation.
Making a convincing guess: empirical evidence
If you can't logically (or "deductively") prove that something is true, maybe you can put together enough evidence to be convinced that something is probably true. For example, even though I can't logically prove that the sun will rise tomorrow, the fact that it has risen every day of my life convinces me that it probably will do what it has always done in the morning. The fact of the sun rising on past occasions is called my empirical evidence, and I am using inductive reasoning (As opposed to deductive reasoning) to draw the conclusion that the sun will come up again tomorrow. Or to use an example that's closer to home, if two student essays use the exact same words and make the exact same mistakes, I can conclude that one of them probably copied from the other. I can't prove it, though. (By the way, "You can't prove it" won't work with me, so don't even try it.) It's usually much easier to show that something is probably true using empirical evidence than it is to prove it is true using deductive logic. However, even inductive reasoning has its limits.
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