Reasoning Skills and Determining Causes Help

Updated on Sep 29, 2011

Introduction to Reasoning Skills and Determining Causes

"Iron rusts from disuse; stagnant water loses its purity and in cold weather becomes frozen; even so does inaction sap the vigor of the mind."

—Leonardo da Vinci, Italian scientist, mathematician, inventor, sculptor, and writer (1452–1519)

Lesson Summary

This lesson will discuss the inductive reasoning approach to determining causes. It will also go over some of the common mistakes in reasoning people make when determining cause and effect.

The lesson Explanations for Arugments Help discussed how explanations are different from arguments. This lesson will look at a specific type of argument: the causal argument. The main difference between an explanation and a causal argument is simply in the way the argument is arranged. In an explanation, like in deductive reasoning, you look at the conclusion ("I was late") and then test the validity of the premises ("because my car broke down"). In a causal argument, on the other hand, the inductive approach is used: Evidence (what happened) is looked at, a conclusion is drawn about the cause based on that evidence, and then the validity of that conclusion is considered.

Just as there are criteria for testing explanations, there are also strategies for evaluating causes. Similarly, just as explanations can use false reasoning, there are also logical fallacies that can be committed in causal arguments. This chapter will start by addressing the two main strategies for determining cause and then discuss how to avoid the fallacies that often go with them.

Determining Cause

When you are presented with an effect and want to inductively determine the cause, there are generally two techniques to use: looking for what's different and looking for what's the same.

Looking for the Difference

Your car wasn't running well on Wednesday. Normally, you use Ultra-Plus gasoline from the station down the street, but on Tuesday, you were low on gas and on cash, so you pulled into a station near your office and got half a tank of the cheapest brand. On Thursday, you went back to your regular station and filled up with your normal gas. By Friday, the car was running fine again. You did nothing else to your car, and nothing else was out of the ordinary.

So what caused the problem?

If you guessed the cheap gasoline, you're probably right. Though there are many things that can go wrong with a car and only a thorough inspection could tell for sure, the given evidence points to the cheap gas as the culprit. Why? Because the cheap gas is the key difference. Let's recap the facts: Your car ran well on your usual gas. When you changed the brand and grade, your car didn't run well. When you went back to your usual gas, your car ran fine again. The difference? The gasoline. Therefore, it's logical to conclude that the gasoline caused your car to run less smoothly.

Though in this example, it's obvious that the gasoline was the key difference, it isn't always so easy to determine causes. Read the following argument:

Every day for the past three months, you've been getting coffee from Lou's Deli, right around the corner from your office. One day, however, Lou's is closed, so you decide to try Moe's Deli across the street. You get your coffee and go to work. An hour later, you have a terrible stomachache. The next day, Lou's is open again and you get your usual coffee. You feel fine the rest of the day. "It must've been Moe's coffee that gave me that stomachache yesterday," you conclude.

This does seem like a logical conclusion, based on the evidence. After all, what's different between today and yesterday? It was Moe's coffee that was the difference, so Moe's coffee was the cause. Right?

Not necessarily. It is quite possible that Moe's coffee did indeed cause your stomachache. However, this conclusion can't be accepted without reservation—you can't say it's likely that Moe's coffee is to blame—until you ask a key question:


Were there any other relevant differences that may have caused the stomachache?

In other words, you need to consider whether there could have been something else that caused your stomachache. For example, maybe late the night before you ate spicy Chinese food. Or maybe you were really nervous about a big meeting that day. Or maybe you skipped breakfast and had an upset stomach to begin with. Any one of these possibilities could have been the cause.

The more possibilities there are, the less confident you should be that Moe's coffee is the culprit. However, if there isn't anything else unusual that you can think of, and especially if you get sick if you try Moe's again, then it's much more likely that Moe's is to blame. Either way, before you pinpoint your cause, be sure to consider whether or not there could be other relevant differences.


One way to sharpen your skill in finding the differences is to practice. Get a book of photographs that are of the same thing with subtle differences built in. See how quickly you can solve each one. It will help you pay closer attention to the details.

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