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7.1: Use reasoning to connect claims and evidence

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    15698
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    Reasoning connects claims and evidence  

    You might remember this from a previous chapter.

    Consider this hypothetical plea from Zach to his father: “Dad, could you loan me money for gas until I get my paycheck at the end of the week? If you do, I’ll be able to haul your junk pile to the dump as well as drive myself back and forth to work. I’ll pay you back as soon as I get my check!”

    Logos appeals to the reader’s intellect. As readers, we test arguments for their soundness. Does the writer make false assumptions? Are there gaps in the argument? Does the writer leap to conclusions without sufficient evidence to back up his claims?

    As writers, we have to build a solid, well-explained, sufficiently supported argument. 

    What about Zach’s argument above? Essentially, he asserts that a loan from his father would benefit both Zach and his dad. Does the argument seem sound? We do not know why Zach is short on cash this week—his father may be aware that Zach spent most of last week’s check on the newest iPhone, so he does not have enough to cover his gas this week. Thus, there may be factors that undermine Zach’s implication that his request is motivated by responsibility. However, he does offer evidence that the loan will allow him to fulfill his obligations.

    We can define our reasoning based on the relationship between our evidence and our claims. We can categorize reasoning into two main categories: Inductive and Deductive

    Inductive Reasoning: Drawing conclusions from patterns of facts

    You likely use inductive reasoning every day. By this kind of logic, we form conclusions based on samples. Lab experiments, for example, must be repeatable in order for scientists to gather a convincing amount of data to prove a hypothesis. If we observe enough examples of an event occurring under similar circumstances, we can employ inductive reasoning to draw a conclusion about the pattern. For example, if we pay less each time we buy apples at Supermart than when we purchase apples at Pete’s Grocery, we will likely conclude, inductively, that apples are less expensive at Supermart.

    When making an argument based on inductive reasoning, a writer will need to

    1) provide evidence to prove the pattern of facts exists

    2) show how the conclusion is valid

    Deductive Reasoning: Drawing conclusions from facts applied to principles

    Deductive reasoning, on the other hand, is drawing a conclusion based on a logical equation. A common example of deductive reasoning is the syllogism: a three part logical statement 

    1. general statement, or major principle: Humans are mortal
    2. minor premise, or observed fact: Plato is human
    3. And a conclusion: Therefore Plato is mortal 

    Persuasion becomes relevant when the issue moves beyond proven facts. As we explore issues of ethics and values, logical reasoning can seem a bit mushy, yet rather than throw up their hands in abandonment of deductive reasoning, humanities scholars generally work hard to establish valid assumptions, or generally agreed-upon notions, that can be used to help humans move closer to reasonable, or logical, social and political beliefs and behaviors.

    More frequently, you will see arguments made in incomplete forms, which is called an enthymeme. An enthymeme seems to “leaps” to its conclusion because it leaves some part of it's logic unstated, and it's major principles are not as universally true. Consider the following examples:

    Enthymeme: Lisa Harmon would be a good hire for our company; she has a degree from Harvard University.

    • Unstated Principle: Anyone with a degree from Harvard University would be a good employee for our company.
    • Observed Fact: Lisa has a degree from Harvard University.
    • Conclusion: Lisa would be a good employee for our company.

    Enthymeme: Kill Bill is a chick flick.

    • Unstated Principle: Any movie that features a female protagonist is a chick flick.
    • Observed Fact: Kill Bill features a female protagonist.
    • Conclusion: Kill Bill is a chick flick.

    In both of these arguments, the writer would need to defend the principle used to reach the conclusion.

    When making an argument based on deductive reasoning, a writer will need to 

    1) establish premises that readers can agree on

    2) draw reasonable conclusions when applying specifics facts to those principles

     

    Adapted from Tanya Long Bennett "Writing and Literature: Composition as Inquiry, Learning, Thinking, and Communication" CC-BY-SA 

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