by Corry Shores
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Argument Diagramming (Open + Free)
Carnegie Mellon University
UNIT 1: Course Introduction
The structural features of arguments can be given visual representation by means of argument diagrams. One complicating factor is that arguments are often embedded in lengthy text, and so they need to be extracted into a simplified format and organized into relations of premise and conclusion. An arrow pointing from a premise to a conclusion indicates that the premise supports the conclusion.
When premises depend on one another for supporting a conclusion, they can be bracketed together and given a single arrow.
UNIT 1: Course Introduction
1.1 What is an Argument Diagram?
Argument diagrams will allow us “to visually represent an argument” in order “to understand and evaluate the argument” (1).
The authors say that we need first to understand “the Big Picture of Argument Diagramming” (1)
They write, “The process of argument diagramming starts when we identify a text that we want to understand. This contains the Argument” (1, emphasis theirs).
They first depict the argument itself with this diagram:
They continue, “An argument is made up of a conclusion and the premises that are supposed to support the conclusion:” (1)
The authors write that arguments are often “embedded in a lot of text”, and they represent this situation in this way: (1)
Now, since the argument is entangled in the text, we might want to disentangle it by making an argument diagram, which “visually displays both the statements and the connections between them, without the clutter of the rest of the text”: (1)
In order to get from the text to the argument diagram, “We can use identifying words (or indicator words) in the text to help us determine which statements are the premises and which is the conclusion:” (1)
After we form the diagram, we can evaluate the argument to see if it is a good or a bad one. “When evaluating, we determine whether the premises are true and whether the premises actually support the conclusion:” (1)
After we establish the truth of the premises and their ability to support the conclusion, “we can offer an overall evaluation of the argument:” (1)
The authors then summarize the entire process with the following description and illustration:
So overall, the process you are going to learn in this course is illustrated below. We investigate the text, using indicators to determine which statements are premises and which is the conclusion, and how they work together. We can then represent the argument as a diagram, which is essentially a representation of our understanding of the argument in the text. Once we have the diagram, we can identify the questions we need to ask in order to evaluate the argument. The answers to those questions allow us to say whether the argument is good or bad.
1.2 Two Motivating Examples
Let us examine the first example, which narrates a situation within which an argument is presented.
“Ten o’clock? I’m not sure if I’ll be able to make it. Let me call you back, okay?” Alexis closed her phone and turned to Brandy, “That was Char. She wants go out to see the Wanderers later. I really want to go…”
“No, you shouldn’t go! Are you kidding? You know we’re going to have a quiz in math tomorrow! You’re not doing so great in the class, and you really should study. Look, I’ll study with you, okay?”
Alexis sighed, “My parents said the same thing. My mom thinks I haven’t been getting enough sleep lately. She wants me to go to bed early. And not just tonight—for the next few.” She sighed again and sat down.
“Well, she has a point.” Brandy sat down too, “Even if we weren’t almost definitely going to have a quiz tomorrow, that’s a good reason why you shouldn’t go.”
“Yeah, maybe,” Alexis trailed off. She flopped back on the bed, “Ugh! You know my dad’s in on it too.”
“What do you mean?”
“He says I’ve been spending too much money. He says the tickets are too expensive. If I want to buy them,” Alexis raised both her hands up to do air-quotes, “I’ll have to ‘crack open someone else’s piggy-bank.’ Ugh,” Alexis sighed again, “But I really want to go!”
Brandy stood up again. “So let me get this straight. You have three separate reasons, and good reasons at that, and you still don’t believe it? That you shouldn’t go out?” Brandy laughed and threw a pillow at her friend, “You’re unbelievable!” She laughed again, as Alexis threw the pillow back.
“You’re right, you’re right. I’m convinced; I won’t go,” Alexis lowered her voice conspiratorially, “but please don’t tell my parents that anything they said made a difference.”
(2, emphasis mine)
We see that the conclusion of the argument is that “Alexis should not go to the concert”, and she has three separate reasons that support this conclusion. The authors diagram this structure in the following way. Note that in the diagram, the upward pointing arrows indicate that the bottom beliefs support the top belief.
The authors then narrate another situation [which we here omit], and the argument within the text can be summarized as:
Lemons contain a combination of citric acid and water.
All combinations of citric acid and water are electrolytes.
So, lemons contain an electrolyte.
Here we have two reasons (the first two lines) and one conclusion. In the prior example, the three reasons operated independently of one another. For, “if one of the reasons were taken away—if, for instance, Char had bought Alexis’ ticket for her—she would still have good reasons to believe that she shouldn’t go out” (2). But here in the second example the two reasons for the conclusion
must work together to support the conclusion. In other words, if we took away the fact that “All combinations of citric acid and water are electrolytes,” then the fact that lemons contain this combination would not be a reason to believe that lemons contain electrolytes (2, emphasis theirs).
So this argument has a structure where the premises operate together rather than in parallel, and we can show that by forming the diagram in this way:
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