Dicto Simpliciter


The argument draws a conclusion from an over-simplistic statement of a rule.



This takes two forms:

Destroying the exception by insisting on the rule, which is usually called Accident, and

Destroying the rule by insisting on the exception, which is sometimes called Reverse Accident, but is classically called Secundum Quid.



Following rules is not, in general a bad idea. Most rules exist for a good reason. Traffic laws prevent accidents; criminal laws keep order in society; even moral rules guide behavior in ways that make our actions (for the most part) effective and socially acceptible. Rules, by their very nature, are intended to be applied to many cases. However, any rule is also bound to have a range of application, and cases falling outside that range are not covered by the rule. Traffic laws designed for downtown Manhattan, for example, may not be particularly suitable for roads in the Australian outback. Cases covered by the same rule must, of course, be similar to each other in important respects, but they cannot be identical to each other in every respect. Red cars and blue cars are not identical, but in downtown Manhattan, both must stop at red lights. In most cases we "just know" when a difference is important and relevant and when it is not, but it is not always easy to explain why. There is no simple criterion for determining when two cases differ so much that they are not covered by the same rule, and when their differences are merely variations within the scope of the rule.

The fallacy of Dicto Simpliciter exploits this difficulty. It asks us to consider cases that are different. One form of the fallacy then tries to pass those differences off as mere variations within the scope of the rule, when they are in fact important and relevant differences. The other form of the fallacy tries to pass those differences off as important and relevant, when they are in fact just variations within the scope of the rule.


Source: The pairing of Accident with Secundum Quid as alternative forms of Dicto Simpliciter is found in August De Morgan's Formal Logic, 1847.


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