Inductive and Deductive Reasoning

Motorcycle Wheel“Inductive inferences start with observations of the machine and arrive at general conclusions. For example, if the cycle goes over a bump and the engine misfires, and then goes over another bump and the engine misfires, and then goes over another bump and the engine misfires, and then goes over a long smooth stretch of road and there is no misfiring, and then goes over a fourth bump and the engine misfires again, one can logically conclude that the misfiring is caused by the bumps. That is induction: reasoning from particular experiences to general truths.

Deductive inferences do the reverse. They start with general knowledge and predict a specific observation. For example, if, from reading the hierarchy of facts about the machine, the mechanic knows the horn of the cycle is powered exclusively by electricity from the battery, then he can logically infer that if the battery is dead the horn will not work. That is deduction.” – Robert Pirsig, ZMM

We use both lines of reasoning all the time without even noticing the differences in the two. Actually, I know that there are a number of times that I don’t even recognize that I am going through any kind of reasoning process. It is a pattern of thought that just comes to me automatically. That is probably a good thing. If I was analyzing every thought in my head all the time, I would be just thinking about what I was thinking about all the time.

But it is important to, occasionally, recognize when you are following a logical line of thought. And most of the time, it will involve inductive and deductive reasoning. Once the reasoning is recognized, you can actually analyze that line of thought further. You can recognize where your logic could be faulty. Take a look at this article for differences in inductive and deductive reasoning.

“Even the best inductive argument cannot claim that the truth of its premises guarantees the truth of its conclusion.” This means that if you recognize that the engine misfires every time you go over a bump, you can only conclude that it is highly likely that the bump causes the misfiring. You should not believe that the bump is 100% guaranteed to cause a misfire every time.

“Even the worst valid deductive argument–that is, one with premises that are actually false–can still claim that if its premises were true, its conclusion would have to be true. No valid deductive argument can guarantee the truth of its premises…” This means that saying “if the battery is dead, the horn will not work” could be a valid deductive argument, but the argument does not tell you if the battery is dead or not. And it is absolutely necessary that the horn not work every time that the battery is dead in order for the “if the battery is dead, the horn will not work” statement to be a valid deductive argument.

So, learning to recognize these types of reasoning helps you learn the rules of logical thought. They tell you what you can and can not say about a subject based on the knowledge that you have. And like I have said previously, there is no such thing as a hard rule. You eventually just choose the rules that you want to believe in. I believe in science, reason and logic. Induction and deduction are fundamental concepts in those fields. I choose to follow those rules.

Photo courtesy of kevygee 

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