1. The fallacy of accident
The fallacy of accident is the first on Aristotle’s list of fallacies independent of discourse, S. Fallacies (II): Aristotle’s foundational list.
The idea is that a valid syllogistic inference develops in the same category domain, for example, the class of animals:
Socrates is a man, man is a mammal, so Socrates is a mammal,
whereas the following fallacious inference develops from an accident:
Socrates is white, white is a color, so Socrates is a color.
The word accident is taken in its philosophical meaning, which contrasts accident with essence. A being is characterized by a set of essential features that determine its place in a scientific classification: its generic features express its genus and its specific difference indicates its species. Unlike “— is a mammal”, which is constantly true of all dogs, the truth of the accidental predicate “— is tired” is circumstantial, it may be true of a dog at a given time but become false as soon as the dog’s condition changes.
The fallacy of accident occurs when an accidental characteristic of a being is mistaken for an essential one. In a definition, the corresponding defect consists in defining a being by a feature which belongs to it only accidentally.
So for example, “— wanders off in the middle of the road” is a relevant definite description, allowing unambiguous reference to a dog, but not a defining feature of « dog”.
All the same, “— is a good time for having a nap” is not a defining feature of “afternoon”, S. Two-term Reasoning.
2. The ad accidens counter-argument
The charge of committing the fallacy of accident is possible only if the accuser can refer to a solid and stabilized categorization, corresponding to a set of essentialist definition, S. Definition (1). In ordinary speech, the accusation of committing a fallacy of accident is just a counter-argument, which opens a stasis of definition and can itself be defeated.
The ethical value of a profession is evaluated on the basis of an examination of the moral worth of its values and practices. In a classical democratic regime, a politician can be honest or dishonest without ever ceasing to be a politician. Dishonesty is not a necessary condition for becoming a politician; it is an accidental feature; “he is an honest politician” is not an oxymoron, “he is a dishonest politician” is not tautologically true. For those sharing this vision of things and people, characterizing political activity as an intrinsically dishonest activity, is committing the fallacy of accident. The person blamed for committing the fallacy might retort that the argument is not based on any transcendental organization of things, but on an inductive generalization, from “a number of politicians we all know very well”; or on the actual structural condition of our political system.
The argument from the opposite, (or a contrario) argument plays with the essential vs. accidental character of the differences between two categories of beings, “boys can go out at night, so girls should not go out, well, you know, girls are different from boys”. It is refuted by demoting the difference from essential to accidental. The same strategy applies to the distinctions between the defining features of a fact, and its circumstantial, contextual characteristics.
Dissociated from the strict Aristotelian ontology, the “essence vs. accident” opposition corresponds to the distinction between central traits and peripheral traits, and, in everyday life, to the distinction between the important and the incidental.
Ultimately, in the absence of backing by an accepted ontology, the so-called fallacy of accident functions as a refutation arguing from the incidental nature of an element, and finally corresponds to a strategy of minimization of the disputed character.