Secundum quid (also called secundum quid et simpliciter, meaning "[what is true] in a certain respect and [what is true] absolutely") is a type of informal fallacy that occurs when the arguer fails to recognize the difference between rules of thumb (soft generalizations, heuristics that hold true as a general rule but leave room for exceptions) and categorical propositions, rules that hold true universally.
Contents
Since it ignores the limits, or qualifications, of rules of thumb, this fallacy is also named ignoring qualifications. The expression misuse of a principle can be used as well.
Example
Water boils at a temperature of 212° Fahrenheit; therefore boiling water will be hot enough to cook an egg hard in five minutes: but if we argue thus at an altitude of 5,000 feet, we shall be disappointed; for the height, through the difference in the pressure of the air, qualifies the truth of our general principle.
Compare with:
In popular culture
The following quatrain can be attributed to C. H. Talbot:
Types
Instances of secundum quid are of two kinds: