Lat. a pari, or a pari ratione, “for the same reason”: par, “equal, same” ratio, “reason”.
A distinction must be drawn between two kinds of a pari arguments, depending on whether they deal with individuals or classes of individuals.
1. When the argument concerns individuals, the a pari argument includes an individual x in a category C. The individual becomes (is identified as) a member of the category, in logical symbols < x ∈ C >, S. Categorization.
2. When the argument concerns classes of individuals, the a pari argument reorganizes the category system (classification@, taxonomy). It reduces two formerly distinct categories (class, species) to one, on the basis that they belong to the same super category (genus). This entry deals with this second definition.
The vocabulary of analogy and the label “argument a comparatione” are sometimes used to refer to the argument a pari, in both of its forms, S. Taxonomies and categories.
The a pari argument “[applies] to another species of the same genus what can be asserted about some particular species.” (Perelman, Olbrechts-Tyteca [1958], p. 241);
A pari reasons by equality of the cases if a parricide deserves death, the same applies to matricide. (Chenique 1975, p. 358)
The a pari argument transfers a property (a quality, a right, a duty…) (here “— deserves death”) originally attached to a species A (here: “— is a parricide”) to another species B (here: “— is a matricide”), arguing that they belong to the same genus (here: “— is a murderer of a parent”). The reasoning is as follows:
The trend is towards severity
The penalty for matricide is life imprisonment.
Let’s strengthen the punishment of matricide!
The penalty for parricide is death.
Parricide and matricide are crimes of the same genus (type, genre, kind…).
The penalty for matricide should be death!
Two different situations should be distinguished for the discussion of a pari.
— Situations of complete knowledge, where the truth is fully known and can be fully contemplated; then, syllogistic reasoning applies.
— Situations where the truth is debatable and a concrete decision has to be made, i.e., argumentative situations.
1. Syllogistic a pari
From the point of view of absolute knowledge, the a pari argument is either a truism or a paralogism, depending on whether or not the property considered is generic, S. Taxonomies and categories.
If the property is generic, then it is true of all species attached to the genus, and particularly true of the two species involved in the a pari argument. The syllogism runs as follows:
Having a constant body temperature is a generic property of mammals.
Whales, humans… are mammals
So Whales, humans… have a constant body temperature.
The corresponding a pari argument is:
Both men and whales are mammals (“belong to the same genus”, here mammals)
Men have a constant body temperature (“what is true of a species”, here humans)
So whales (must) have a constant body temperature (“is applied to another species”, here whales).
If the property is not generic, then, the inference is a paralogism:
Labradors, poodles… are dogs
Labradors are gun dogs
So, poodles are / must be gun dogs.
The corresponding a pari argument is:
Both labradors and poodles are dogs (“belong to the same genus” here dogs)
Labradors are gun dogs (“what is true of a species”, here labradors)
So poodles are gun dogs (“is applied to another species”, here gun dogs).
But poodles are not gun dogs. The property “— is a gun dog” is not a generic property, it is attached to labrador as a species, not to the genus “dogs”. It follows that this property cannot be safely transferred to poodles.
In short, a property can be transferred from a species to another species belonging to a same genus only if the said property is generic. The validity of the argument depends on the quality of the taxonomy it exploits, and the argument will be considered convincing only if people agree on the classification.
2. The seeming deadlocks a pari vs. a contrario
and a pari vs. a pari
Two paradoxes are attributed to a pari argument. In the same situation:
- a contrario and a pari cancel each other out;
- a pari can destroy a pari.
2.1 A contrario against a pari
(i) A pari extends to the As the treatment given to the Bs, arguing that both are attached to a common super-category:
(1) the As are like the Bs! they should be treated as Bs!
(ii) A contrario, the argument from the opposite, justifies the difference in treatment of the As and Bs, arguing that they are indeed opposites:
(2) The As and Bs are different, so they are rightly treated as such!
In both cases, the question is whether a difference between A and B should be preserved: a contrario answers “yes!”, a pari answers “no!”.
2.2 A pari against a pari
A pari argument extends to B a characteristic of A, or to A a characteristic of B. It can be objected to (i):
(3) If the As are like the Bs, then the Bs are like the As; the Bs are the ones which should be treated like As!
Here, proponent and opponent refer to the same data and use the same rule to support contrary claims. They agree on the necessity to re-categorize As and Bs into just one category, but disagree about which should prevail.
Hence the conclusion may be reached that all this maneuvering is useless (in the following quotation “analogy” means a pari):
That the argumentum a contrario and analogy as means of interpretation are entirely worthless can be seen from the fact that both lead to opposite results, and that no criterion exists to decide when the one and when the other should be applied. (Kelsen 1967, p. 352).
This is the case for an abstract, syllogistic situation, where:
— A contrario is actually logically invalid, S. Opposites – A contrario.
— A contrario can be systematically opposed to a pari.
— As a “bidirectional” argument scheme, a pari can always be opposed to a pari.
3. Argumentative a pari and the situated condition of argument
Let us schematize a situation in which Gs and Bs are treated differently. A pari can be used to support the claims “All Gs!” or “All Bs!” and a contrario, to rebut both.
| Present situation | Revendication |
| all Gs! | |
| G ≠ B and G and B are treated differently | |
| all Bs! |
— A contrario is the status quo argument, which may be set up against both a pari alignments. Those arguing for a status quo do not support the burden of proof, they can simply reformulate and amplify the current “doxical” discourse, to maximize the opposition between As and Bs, and so to justify a contrario the difference in treatment:
It is not by chance that As and Bs are called A and B, precisely because they are A and B, and not something else!
— The proponent of either a pari alignments of categories must undermine this discourse, showing that the difference formerly considered as essential should now be considered a mere accident. These minimizing strategies accompanying a pari depend on the characteristics of the specific situations.
In a slightly more complicated move, the individual forwarding an a pari argument may attempt to show that it is possible to construct a super category, including both A and B. This solution implies that the former definitions of both categories needs to be amended.
The problem with the syllogistic approach of a priori is that it does not take the argumentative situation into account, whereas there are preferences and impossibilities enshrined in any such situation. These contextual conditions systematically eliminate one or the other application of a pari. A pari is logically bi-directional and contextually mono-directional, as can be seen in the following cases.
3.1 Military service: girls / boys
Context: a country where boys, but not girls, complete compulsory military service. Applying a pari to the boys, that is, claiming that they should not do their military service, amounts to requesting the dissolution of the army, its professionalization, or similar. This would be the real issue, and not that of equal treatment of boys and girls.
So, the a pari argument can only be advanced by the girls, or by the military administration willing to incorporate girls. The relevant argumentative question can only be “should the girls do military service too?”, and a pari backs a positive answer very well.
3.2 Murders: patricide / matricide
Context: a social situation in which a “civilizing process” is taking place; there is a clear effort being made to eliminate all forms of violence. In such a situation, an a pari generalization of the death penalty is “out of the question”. The only relevant issue can be “should we reduce the penalty for patricide?”, with a pari being used to back a positive answer.
If the social climate is oriented towards the strengthening of penalties, the situation is the same, with a pari serving as justification for the positive answer to the question “should we increase the penalty for matricide?”.
3.3 Employment: fixed-term / permanent contract
Context: Some employees receive a Permanent Contracts (PC), while others have a Fixed Term Contracts (FTC), the former kind of contracts being considered better than the latter from the point of view of the workers. In a period of prosperity and full employment, PCs are the golden standard, the a pari alignment of FTCs with PCs is on the agenda. The issue of a possible alignment of PCs with FTCs is irrelevant. The difference will be denied through argumentations such as:
People with FTCs are exploited, we are all workers, everyone should be able to get a PC!
In less favorable economic conditions, FTCs become the norm, and their alignment with PCs is not on the agenda. The difference will be denied by argumentations such as:
People with PCs are privileged, privileges should be ended, everyone should be put on an FTC!
3.4 Going out at night: girls / boys
Let us consider a family of consisting of both teenage boys and teeenage girls, two species of the same genus. The boys are authorized to go out in the evening, the girls however are not. Let us suppose that this prohibition annoys the girls. They can argue their point in many ways. They might, for example draw on the positive outcomes that going out at night will have on their social awareness, S. Pragmatic argument; they might also point out that their brothers go out at night, in an elliptic a pari:
G — But the boys do go out at night!
Unsurprisingly, the parents argue a contrario:
P — Yes but you are a girl…
To strengthen their case and eliminate the difference, girls might stress the common features characterizing the new catchall category “as the boys”:
Boys and girls receive the same education; they have access to the same media; they practice judo; they follow the same courses with the same requirements; they share the same tasks at home …
and minimize the gender gap:
We are mature, we know how to avoid trouble.