Chapter 5 Flashcards — Deduction and Induction: The Difference
flashcards tpp deduction induction logical-reasoning key-line argument-structure
What are the only two forms of logical reasoning available for relating ideas sideways in a pyramid?
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Deduction and induction. These are the only two patterns available for establishing logical relationships between ideas at the same level of the pyramid. Understanding how they differ and what their rules are is essential to sorting out your thinking and expressing it clearly in writing.
What is the defining characteristic that distinguishes deduction from induction?
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In deduction, the points derive from each other — each step comments on the subject or predicate of the previous step, leading to a “therefore” conclusion. The top-level summary rests heavily on the final point. In induction, the points do NOT derive from each other — they are independently observed members of the same class, and the top-level point makes an inference about their sameness.
What are the three steps of a deductive argument (Minto’s formulation, not the classic syllogism)?
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- Make a statement about a situation that exists in the world.
- Make another statement about a related situation that exists in the world at the same time (the second statement relates to the first by commenting on either its subject or its predicate).
- State the implication of these two situations existing in the world at the same time (the “therefore” conclusion).
What is the “plural noun test” for inductive reasoning?
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Find one word — a plural noun — that describes the kind of idea shared by all items in the grouping. The word will always be a noun (any “kind of” thing is a noun) and always plural (because you will always have more than one). If you can find a single plural noun that accurately describes every item in the grouping, and there are no misfits, the inductive grouping is valid. Examples: “schemes,” “steps,” “ways of hurting.”
Why is deductive reasoning a ponderous way to write at the Key Line level?
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Because the reader must hold multiple threads simultaneously before receiving the payoff. In a structure of “Here’s what’s wrong → Here’s what’s causing it → Therefore here’s what you should do,” the reader must (1) absorb the full list of what is going wrong, (2) mentally match each cause to each problem, and (3) hold all that in mind before finally receiving the recommendation. The reader waits a very long time to find out what he should do — it is as if you say “I worked extremely hard to get this answer, and I’m going to make sure you know it.”
In what two situations should you use a deductive argument at the Key Line level?
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- When the point at the top of the pyramid is alien to what the reader expects — e.g., the reader asked “How do I cut costs?” but you say “You should sell the business.” Here the reader must understand the argument before the action makes sense.
- When the reader is incapable of understanding the action without prior explanation — e.g., the reader needs to understand the reasoning behind an analytical approach before he can execute the steps.
What are the rules for chaining deductive arguments?
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(a) No more than four points in a single deductive argument. (b) No more than two “therefore” points in a chained argument. You can violate these rules, but the groupings will become too heavy to summarize effectively — the point at the top will not be able to accurately summarize the ideas grouped below. Chaining is only valid when the reader is likely to grasp and agree with the steps being skipped.
How does the Recommendation Worksheet (Exhibit 19) illustrate the difference between deductive and inductive presentation?
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The worksheet has three columns: Findings (what’s going wrong) → Conclusions (what’s causing it) → Recommendations (what to do). This is always a deductive structure — each column’s ideas derive from the previous column. To present deductively, read the columns left to right. To present inductively, rotate the worksheet 90 degrees: the Recommendations (A3, B3, C3) go on the Key Line, and the supporting Findings/Conclusions are grouped underneath each recommendation. Inductive presentation answers the reader’s question immediately.
What is the quick test for whether two ideas are deductively or inductively related?
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If the second idea comments on the subject or predicate of the first idea, they are deductively related. If the second idea does NOT comment on the first but both can be described by the same plural noun, they are inductively related. If neither applies, the ideas do not belong together in a grouping.
What are the two patterns for building inductive arguments, and what does each produce?
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- Hold the subject constant, vary the predicate: “Japanese businessmen are escalating their drive for the Chinese market / Indonesian market / Australian market.” → Inference: “Japanese businessmen are moving aggressively into Southeast Asia.”
- Hold the predicate constant, vary the subject: “Japanese/American/German businessmen are escalating their drive for the Chinese market.” → Inference: “The smart money is moving into China.”
If there is no common thread at all (neither subject nor predicate relates), there is no valid inference — you are just passing along news, which has no place in a document whose purpose is to communicate thinking.
What is the danger of a top-level inductive statement that “goes beyond the grouping”?
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If the inference at the top cannot be specifically and only derived from the items grouped below, the reasoning is invalid. Example: “Managers mismanage because they want to” cannot be validly inferred from a list of mismanagement behaviors (don’t face reality, won’t countenance criticism, etc.) — you can describe the behaviors but cannot validly infer intent. The inference must be specific to those items and not go beyond them. If the top-level point is too abstract, it likely means the items are actually part of a deductive chain masquerading as an inductive group.
When do you have a deductive argument masquerading as an inductive one?
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When you have only one piece of evidence for your conclusion and you are forced to reason through a cause-and-effect chain. Example: “Composing room costs represent a profit-improvement opportunity” with three supposed “indicators” (productivity low, overtime high, prices uncompetitive) — this is really a deductive chain: low productivity → high overtime → uncompetitive prices. Whenever you have only one piece of evidence for anything, you are forced to deal with it deductively. The point implied at the top is something like “Our prices are high because our productivity is low.”
What does the mind automatically expect when it encounters either an inductive grouping or the beginning of a deductive chain?
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The mind automatically expects either a summarizing statement (for inductive groups) or a “therefore” point (for deductive chains). This expectation leads the reader to project his thinking ahead — to formulate what he thinks the next point will be. If his projected point differs from your actual point, he becomes confused and annoyed. This is why you must always give the reader the top-level point before stating the ideas grouped below — to orient his expectations correctly.
What is the distinction between “news” and “thinking,” and why does it matter for inductive groupings?
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News = a true fact that does not relate to other facts in a group in a way that enables you to draw a general inference. Thinking = ideas that together help explain or defend a higher-level point. The fact that a point is true is not sufficient justification for including it in a document. Only a legitimate inference (specific to the grouped items) counts as thinking. Passing along unrelated true facts (“news”) without being able to draw an inference from them violates the basic justification for including a point in a pyramid.