Inductive Reasoning Help (page 2)
Introduction to Inductive Reasoning
"A man who does not think for himself does not think at all."
—Oscar Wilde, Irish playwright, poet, and author (1854–1900)
In this lesson, you'll review the difference between deductive and inductive reasoning. You'll also sharpen your inductive reasoning skills by learning how to draw logical conclusions from evidence.
The lesson Inductive vs Deductive Reasoning Help explains the difference between inductive and deductive reasoning. In deductive reasoning, as you know, an argument moves from a conclusion to the evidence (premises) that supports that conclusion. Inductive arguments, on the other hand, move from evidence to a conclusion drawn from that evidence.
As a critical thinker, when you come across a deductive argument, you should examine the validity of the evidence for the conclusion. If the evidence is valid, the conclusion—and therefore the whole argument—is a good one. However, in inductive reasoning, the goal is not to test the validity of the evidence. Rather, it is to examine the validity of the conclusion. If the conclusion stems logically from the evidence, then the argument can be considered a good one.
But how do you know if the conclusion is logical? In inductive reasoning, the main criterion is to determine the likelihood that the premises lead to the conclusion. Likelihood can be judged based on:
- Common sense
- Past experience
Of course, formal logic, involving mathematical symbols, can also help, but that won't be discussed in this book.
Here's an example of a brief inductive argument:
Due to a storm, there was a major power-outage last night in a nearby town. A lot of people must have used flashlights and lit candles to see.
If the premise that there was a major power-outage in a nearby town is true, is it reasonable to assume that a lot of people lit candles and used flashlights to see? What do you think—is a power-outage at night likely to cause people to turn on flashlights and light candles? Based on common sense and past experience, you can say with confidence yes. Is it very likely? Again, you can confidently say yes. Therefore, this is a good inductive argument—a logical conclusion drawn from common sense and past experience; or substantial evidence.
The Science of Inductive Reasoning
Any time someone draws conclusions from evidence, inductive reasoning is being used. Scientists use it all the time. For example, let's say a scientist takes two equally healthy plants of the same size, age, and type. She puts Plant A in a room with a radio that plays only classical music. She puts Plant B in a room with a radio that plays only rock and roll. Both plants receive equal light and water. After six weeks, Plant A has grown six inches. Plant B, on the other hand, has grown only three inches, which is the average growth rate for these types of plants. She repeats this experiment and gets the same results. Using her inductive reasoning skills, what is the most logical thing for the scientist to conclude?
- In both cases, Plant B must not have been as healthy to start as Plant A.
- Plants grow better when exposed to classical music than to rock and roll.
- Rock and roll music stunts plant growth.
Well, common sense would suggest that choice a isn't an option, because it is stated that both plants were equally healthy at the start of the experiment. Furthermore, since it is known that Plant B grew at the normal rate, then c can't be a logical conclusion either. But even without this process of elimination, common sense and the results of the two experiments point to conclusion b, that plants grow better to classical music than to rock and roll. (This is true, by the way!)
Of course, this conclusion would be even more valid if the scientist repeated the experiment several more times and continued to get the same results. The more she performs the experiment and gets the same results, the stronger her argument will be.
Many of the concepts in reasoning and logic are also used in different mathematical concepts. With inductive reasoning, you can think of it as a type of formula with Logical conclusion = common sense + past experience + substantial evidence
Inductive Reasoning in Practice
Detectives, like scientists, also use inductive reasoning. In the following excerpt from the story "The Reigate Puzzle," for example, the famous fictional character Sherlock Holmes uses inductive reasoning to solve a tricky crime. By examining a piece of a torn document, he is able to conclude that two different men wrote the document, and he's able to determine which of the two men is the "ringleader." Read how he does it:
"And now I made a very careful examination of the corner of paper which the Inspector had submitted to us. It was at once clear to me that it formed part of a very remarkable document. Here it is. Do you not now observe something very suggestive about it?" [said Holmes.]
"It has a very irregular look," said the Colonel.
"My dear sir," cried Holmes, "there cannot be the least doubt in the world that it has been written by two persons doing alternate words. When I draw your attention to the strong t's of 'at' and 'to,' and ask you to compare them with the weak ones of 'quarter' and 'twelve,' you will instantly recognize the fact. A very brief analysis of these four words would enable you to say with the utmost confidence that the 'learn' and the 'maybe' are written in the stronger hand, and the 'what' in the weaker."
"By Jove, it's as clear as day!" cried the Colonel. "Why on earth should two men write a letter in such a fashion?"
"Obviously the business was a bad one, and one of the men who distrusted the other was determined that, whatever was done, each should have an equal hand in it. Now, of the two men, it is clear that the one who wrote the 'at' and 'to' was the ringleader."
"How do you get at that?"
"We might deduce it from the mere character of the one hand as compared with the other. But we have more assured reasons than that for supposing it. If you examine this scrap with attention you will come to the conclusion that the man with the stronger hand wrote all of his words first, leaving blanks for the other to fill up. These blanks were not always sufficient, and you can see that the second man had to squeeze to fit his 'quarter' in between the 'at' and the 'to,' showing that the latter were already written. The man who wrote all his words first is undoubtedly the man who planned the affair."
Notice how Holmes looks carefully at the document and uses what he sees to make logical inferences (draw logical conclusions) about the two men responsible for the crime. The difference in the t's indicates two different writers and the uneven spacing of the words indicates who wrote first, thus leading Holmes to conclude that the man who wrote first was the man "who planned the affair."
To practice your ability to use inductive reasoning, try reading a few of Arthur Conan Doyle's short stories about Sherlock Holmes and watch for the clues. Underline or highlight them as you read (not in library or school books!) and then see if you can figure out the solution before Holmes does.
Inductive Reasoning In Short
Inductive reasoning is the process of drawing conclusions from evidence. A good inductive argument is one in which it is very likely that the premises lead to the conclusion. Past experience and common sense can be used to measure that likelihood.
Skill Building until Next Time
- Notice how often you use inductive reasoning throughout your day. At home, work, or school, as you travel from place to place, what conclusions do you draw from what you see around you?
- Read a detective story or watch a detective show like Without a Trace, NYPD Blue, or Law & Order. Pay special attention to how detectives use evidence to draw conclusions about the crime.
Exercises for this concept can be found at Inductive Reasoning Practice.
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