Formal and Informal Fallacies

“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 namesĀ 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.

Formal Fallacies

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.”

Informal Fallacies
  • False dilemma
  • May/Must fallacy (surprisingly, Wikipedia has no entry for this)

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