All the chewy goodness of fallacious reasoning in new fun-sized bites!

Post hoc ergo propter hoc in latin means “after this, therefore because of this.” It often takes the abbreviated form of post hoc.

A post hoc fallacy is a variant of the fallacy of false cause (which most simply means confusing a cause with an effect). According to John Nolt et al., a post hoc fallacy takes place when “a causal relationship is inferred merely from the temporal proximity of two or more events.”[1] All false-cause fallacies, including post hoc, feature causal claims that are inadequately supported by their premises.[2]

In other words, a superstitious person might say, “Every time my left hand itches, money arrives in the mail!” Let’s allow for a moment that money actually does arrive in the mail every time that person’s left hand itches. That would make these two events: 1) the person’s left hand itching and 2) money arriving in the mail close in temporal proximity; but it obviously is highly unlikely that itching hands cause money to arrive in mailboxes. Therefore, this old wive’s tale is an example of a post hoc fallacy.

Consider this example:

All prophets from Scripture displayed charismatic leadership.
Therefore, charismatic leadership causes prophecy.

Again, these two features (charismatic leadership and prophecy), while close in temporal proximity, are unlikely to be causally linked, especially considering Scripture’s explanation for the true source of prophecy (i.e. God).

According to Nolt, there is an important qualification to consider with regard to post hoc fallacies: A post hoc fallacy is inductive. In other words, just because a particular line of reasoning is labeled as post hoc does not automatically mean that its conclusion is false. “It means merely that the evidence contained in the premises does not by itself make the conclusion very probable.”[3] As always take great care when reasoning through these issues.

The best way to point out someone’s fallacy is by using the Columbo tactic as laid out in the Funsized Tactics series. There are plenty of excellent resources available in book, e-book, or PDF format. Two good places to start, with regard to formal and informal fallacies, are A Preface to Philosophy by Mark B. Woodhouse and Schaum’s Outlines: Logic by John Nolt, Dennis Rohatyn, and Achille Varzi.

[1] John Nolt, Dennis Rohatyn, and Achille Varzi, Schaum’s Outlines: Logic, 2nd ed. (New York: The McGraw-Hill Companies, 2011), 210.

[2] Ibid.

[3] Ibid.

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