Episode #7 of the course Logic basics: Understanding arguments by Gary Curtis
Over the last two lessons, you’ve taken scenic detours to study the difference between induction and deduction, and between arguments and explanations. Today, you’ll return to the main route, putting what you learned in previous lessons to use in analyzing argument structure.
When analyzing an argument, try not to evaluate it until you have fully analyzed it. Mistakes in argument evaluation can result from skipping the analysis step, rushing through it, or allowing a premature evaluation to prejudice the analysis.
For this lesson, you will analyze a short passage that contains only a single argument and nothing else. This is quite unrealistic, since most arguments come embedded in longer passages that contain non-argumentative material. Moreover, arguments are often linked together, as we will see in upcoming lessons. However, it’s useful to start by analyzing simple examples.
To analyze the structure of an argument, use argument indicators to determine what the premises and conclusion are. If every premise of an argument came labeled with a premise indicator and every conclusion with a conclusion indicator, or if the conclusion always came at the end of the argument, argument analysis would be easy. What makes it difficult is the fact that some premises or the conclusion will not be marked―occasionally, none of them will be―and the conclusion may not come at the end.
So, it’s helpful, at least at first, to follow these steps in analyzing an argument:
1. Identify the statements. How many statements are there in the argument? You might underline and number them.
2. Identify indicators: Are there any argument indicator words or phrases? Are they really functioning as argument indicators? Remember from Lessons 3 and 4 that such words and phrases often have other meanings. If there are argument indicators in a passage, then there is at least one argument.
3. Identify conclusion indicators: Is there a conclusion indicator? If so, which statement does it indicate as the conclusion?
4. Identify premise indicators: Are there any premise indicators? If so, which statements do they indicate are premises?
5. If there are no indicators, use your understanding of what is being said: Is the passage making a case for some claim? If so, that claim is the conclusion. You may also be able to tell whether the statements are premises or conclusions by a process of elimination or by their position in the passage.
6. Finally, reconstruct the argument and check to see whether it makes sense. You can reconstruct the argument by listing its premises and conclusion.
Here’s a simple example to illustrate these steps:
“Since the blackmailer was a man, it follows that she cannot be the blackmailer.” (Source: Agatha Christie, The Murder of Roger Ackroyd)
1. This is a single grammatical sentence, but it has two clauses that make statements:
a. The blackmailer was a man.
b. She cannot be the blackmailer.
2. There are two argument indicators: “Since” and “it follows that.” So, this is an argument.
3. There is one conclusion indicator, which is, “it follows that.” It indicates that statement b is the conclusion.
4. There is one premise indicator: “Since.” It indicates that statement a is the premise.
5. There are no unmarked statements.
6. The argument is from premise a to conclusion b, and it makes perfect sense: If the blackmailer was a man, then he wasn’t a woman; therefore “she”—whomever she is, she is a woman—can’t be the blackmailer.
Having learned to analyze the structure of arguments, in the next lesson, you’ll begin studying how to evaluate them.
Logic Made Easy: How to Know When Language Deceives You by Deborah J. Benne
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