This Week in Posterior Analytics
We at Organon would like to recognize Jonathan Chait for excellence in the application of Aristotelian logic in public discourse for his post yesterday describing the fallacy of Affirming the Consequent. Chait sketches the form of the fallacy like this:
If A, then B.
B.
Therefore, A.The first two parts (if A, then B, and B) can be true. The fallacy comes in concluding that A is true.
He then breaks down an example from a recent post by Joe Klein at Time’s Swampland:
If [A] Gingrich is running for office, then [B] he will act dumb and angry.
[B] Gingrich is acting dumb and angry.
Therefore, [A] Gingrich is running for office.
The problem is treating material implication (If A, then B) as if it were material equivalence (B, if and only if A). As Chait explains:
Klein proceeds to elaborate that Gingrich will occasionally say something rational when not running for office. Even if we assume that this is true, this is a far weaker claim than saying that Gingrich will exclusively say rational things when not running for office. And that strong claim is necessary to infer that Gingrich is running for office from the fact that he said something dumb and angry. My view is that Gingrich says dumb, angry things constantly and without regard to electoral ambitions. [Ad hominem summation censored.]
Posterior Analytics
All instruction given or received by way of argument proceeds from pre-existent knowledge. This becomes evident upon a survey of all the species of such instruction. The mathematical sciences and all other speculative disciplines are acquired in this way, and so are the two forms of dialectical reasoning, syllogistic and inductive; for each of these latter make use of old knowledge to impart new, the syllogism assuming an audience that accepts its premisses, induction exhibiting the universal as implicit in the clearly known particular. Again, the persuasion exerted by rhetorical arguments is in principle the same, since they use either example, a kind of induction, or enthymeme, a form of syllogism.
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