“Flaw” questions involve one of three types of errors–faulty assumptions, logical errors (technically known as “formal fallacies”), and other types of faulty reasoning (the “informal fallacies”). Unscrupulous people have exploited these fallacies for so many centuries that most of them have their own Latin names and all of them have their own Wikepedia page. The following is a list of fallacies that have appeared on LSAT preptests, in alphabetical order by Wikipedia entry.
Most logicians use the term “antecedent” for the first term in a conditional statement and “consequent” for the last term. The LSAT never uses these terms, however. All LSAT materials call the “antecedent” the “sufficient term” and the “consequent” the “necessary term.”
- False dilemma
- May/Must fallacy (surprisingly, Wikipedia has no entry for this)
“Flaw” type questions come in three basic forms–assumptions, logical errors, and fallacies. Doing well on flaw questions means doing well on each of these three very different challenges.
Assumptions are easiest for people with no special training in logic. It is easy to spot an assumption type answer, since it tends to start with a phrase like “fails to consider that” or “takes for granted that.” In a typical assumption scenario, the answer choice will provide a new fact that would make a big difference to the argument. You don’t need to be a logic whiz to figure out how that new fact might change things. Since each assumption-type answer is unique to the facts in that particular argument, there is no easy way to train up to do better on assumption answers.
Logical errors, by contrast, do not involve new facts. They are technically known as “formal fallacies,” which means they are wrong because of the “form” of the argument. Any “formal fallacy” can be reduced to symbolic logic so that the actual terms under discussion no longer matter. A stimulus that says “Albion is in Britain” can be rewritten as “A->B.” In a “formal fallacy,” it doesn’t matter whether “B” stands for “Britain” or “Botswana.” For example, if I say “I am in Britain, therefore I am in Albion,” I have committed the logical error that PowerScore refers to as a “mistaken reversal.” To do well on this type of flaw question, you need to do well on conditional logic as a whole. I am working on a flashcard deck for logical errors.
The third type of flaw is a specialized version of logical errors that cannot be reduced to symbolic logic. These “informal fallacies” involve a host of tricks and traps for the unwary. Unscrupulous people have been using these fallacies to dupe people for so many centuries that most of them have Latin names. These Latin names never appear on the LSAT, which adds an unintended degree of difficulty to the test. The LSAT answer choices that describe these informal fallacies can be more bewildering than Latin, especially to people who have some familiarity with the traditional names. To address this problem, I am working on two sets of informal fallacy flash cards–one that identifies all the most common and/or recent fallacies by their Wikipedia names, and another which then connects those names to wording that mimics the LSAT answer choices.
- List of fallacies
- Fallacy flashcards
- Flaw answer choices