The Little Blue Reasoning Book - Brandon Royal [28]
Conclusion: I shop at Big-Buy grocery stores.
Evidence: Prices are 10% less.
Assumption: Price is the decisive factor in determining where I shop for groceries. Or stated more simply, when choosing between Big-Buy and Quick-Stop, I choose based on price.
Let’s attack the argument:
Attack the evidence
Are prices really 10% less at Big-Buy grocery stores? Are prices even cheaper at all? We need proof. Perhaps it’s time to check grocery receipts to verify claims of lower prices. Don’t just take for granted that all evidence is really “good” evidence. Moreover, is quality constant? If the quality of two items is different, better quality might warrant paying higher prices.
Attack the assumption
For example, we may want to attack the assumption by saying that price should not be the motivating factor as to where we shop. Perhaps location or proximity is a better criterion, or perhaps customer service should be the key factor influencing where we shop; perhaps store appearance and cleanliness should be the determining factor; perhaps prestige is the driving factor.
THE FIVE COMMON REASONING FLAWS
Tip #22: The five most common critical reasoning errors include: comparing “apples with oranges,” over-generalizing on the basis of small samples, ignoring relevant evidence, confusing cause and effect, and failing to anticipate bottlenecks when plans are put into action.
When we speak of critical reasoning errors, we are referring largely to errors relating to the assumptions we make. Of the five common types of assumptions, the first category falls under comparison and analogy assumptions and requires that we compare two things which, although different, are logically equivalent. In general, we want to compare apples with apples and oranges with oranges, without mixing the two. The second category falls under representativeness assumptions. This reasoning error involves overgeneralizing on the basis of small samples or limited experience. In making the assumption that a sample is representative of the larger whole, we strengthen an argument. In making the assumption that the sample is not representative of the larger whole, the overall argument is weakened. The third category falls under “good evidence” assumptions. This reasoning error occurs when we take for granted that the evidence chosen is valid. The assumption that evidence chosen is objective, typical, and truthful serves to strengthen any argument; the idea that evidence chosen is subjective, atypical, or spurious serves to weaken any argument. The fourth category falls within the topic of cause-and-effect assumptions. This reasoning error occurs if we mistakenly match cause with effect, or assume, without adequate evidence, that one event is the cause of another. The fifth category falls under implementation assumptions. This reasoning error arises from not anticipating bottlenecks when plans are put into action, and occurs whenever we assume outright that plans can be turned into action without significant impediments.
Comparison and Analogy Assumptions
We make comparisons based on people, places, things, or situations. Often it is done through analogy. What is an analogy? An analogy is a comparison of two (or more) items made on the basis that because they share one or more similarities, we can therefore assume they are alike in one or more other respects. An analogy is created every time a researcher delves into the realm of biological experimentation and compares the results done on animals, usually mice, to human beings. Sometimes, the comparison involves personal characteristics. We may see certain traits or characteristics in a father and son or mother and daughter and believe it is the basis for their sharing other similar characteristics. Other times, the comparison involves comparing two situations or events over different time periods. Many corporate decisions are still based on the idea that what has worked in the past will work in the future. International law is also, in large part, based on the