A recent exchange on It Affects You made me realize that a great many of my most frustrating moments online are related to a single family of logic errors. Many people seem to have trouble with the idea that “A implies B” is not the same as “B implies A” and that refuting the latter (by showing an example of “B but not A”) does not refute the former. Similarly, saying that A causes B is not the same as saying that only A causes B. Here are some more concrete examples.

  • Statement: human activity promotes global warming
    Misinterpretation: all global warming is caused by human activity
    Pseudo-refutation: global warming exists on Mars without human activity, so human activity is irrelevant to global warming
  • Statement: this crash was caused by X, which I fixed
    Misinterpretation: all crashes like this are caused by X
    Pseudo-refutation: I just saw a crash without going anywhere near X, so your fix doesn’t work
  • Statement: lack of access to education prevents people from getting off welfare
    Misinterpretation: education is a sure route to getting off welfare
    Pseudo-refutation: Joe Bloggs had access to education but ended up on welfare anyway

This kind of argument is in one sense a kind of strawman, attacking a claim that was actually never made, but “strawman” is a general term that can apply to several kinds of logic errors if you look at them the right way. A little more specifically, many such arguments can be recognized by the original claim being about some X while the response assumes all or none. One term for it is denying the antecedent but people who have trouble understanding implication/causation or some/all/none won’t exactly understand why that’s wrong. I therefore suggest “inversion” as a term for this particular (il)logical construct.