{"id":4335,"date":"2021-07-29T18:55:11","date_gmt":"2021-07-29T16:55:11","guid":{"rendered":"http:\/\/icar.cnrs.fr\/dicoplantin\/?p=4335"},"modified":"2025-08-05T17:30:15","modified_gmt":"2025-08-05T15:30:15","slug":"a-pari-eng","status":"publish","type":"post","link":"https:\/\/icar.cnrs.fr\/dicoplantin\/a-pari-eng\/","title":{"rendered":"A pari \u201cfor the same reason\u201d"},"content":{"rendered":"

A PARI<\/span> argument<\/span><\/h1>\n

Lat. a pari, <\/em>or a pari ratione<\/em>, \u201cfor the same reason\u201d: par<\/em>, \u201cequal, same\u201d ratio<\/em>, \u201creason\u201d.<\/p>\n

There are two types of a pari arguments, depending on whether they deal with individuals or classes of individuals.<\/p>\n

1. When the argument concerns individuals<\/em>,<\/strong> the a pari<\/em> argument includes an individual x<\/strong> in a cate\u00adgory<\/em> C<\/strong>. The individual becomes (is identified as) a member of the category; in logical symbols < x \u2208 C >, see. categorization<\/a>.
\n<\/strong><\/p>\n

2. When the argument concerns classes <\/em>of individuals,<\/strong> the a pari<\/em> argument reorganizes the cate\u00adgory system (classification<\/a>, taxonomy). It reduces two formerly distinct categories (class<\/em>, species<\/em>) to one, on the basis that they belong to the same supercategory (genus<\/em>). This entry is about this second definition.<\/p>\n

The vocabulary of analogy and the label \u201cargument a comparatione<\/em>\u201d are sometimes used to refer to the argument a pari<\/em>, in both its forms, see. taxonomies and categories<\/a>.<\/p>\n

The a pari<\/em> argument \u201c[applies] to another species of the same genus what can be said about some particular species.\u201d (Perelman, Olbrechts-Tyteca [1958], p. 241).<\/p>\n

A pari <\/em>reasons by equality of the cases if a parricide deserves death, then so does the matricide. (Chenique 1975, p. 358)<\/p>\n

The a pari <\/em>argument transfers a property (a quality, a right, a duty\u2026) (here \u201c\u2014\u00a0deserves death<\/em>\u201d) originally attached to a species<\/em> A<\/strong> (here, \u201c\u2014\u00a0is a parricide<\/em>\u201d) to an\u00adother species<\/em> B<\/strong> (here, \u201c\u2014 is a matricide<\/em>\u201d), arguing that they belong to the same genus<\/em> (here: \u201c\u2014\u00a0is a murderer of a parent<\/em>\u201d). The reasoning is as follows:<\/p>\n

The tendency is toward severity
\nThe penalty for matricide is life imprisonment.
\nTherefore, let’s increase the penalty of matricide!<\/p>\n

The penalty for parricide is death.
\nParricide and matricide are crimes of the same genus (type, genre, kind\u2026).
\nThe penalty for matricide should be death!<\/p>\n

For the general discussion of a pari, <\/em>two different situations should be distinguished.
\n\u2014 Situations of complete knowledge, where the truth is fully known and can be fully considered; then, syllogistic reasoning applies.
\n\u2014 Situations where the truth is debatable and a concrete decision must be made, i.e., argumentative situations.<\/p>\n

1. Syllogistic A Pari<\/em><\/span><\/h1>\n

From the point of view of absolute knowledge, an a pari<\/em> argument is either a truism or a paralogism, depending on whether or not the property under consideration is generic or not, see taxonomies and categories.<\/a><\/p>\n

If the property is generic<\/strong><\/span>, then it is true for all species belonging to the genus, and especially for the two species involved in the a pari<\/em> argument. The syllogism is as follows:<\/p>\n

Having a constant body temperature is a generic<\/em> property of mammals.
\nWhales, humans… are mammals
\nSo<\/em> <\/strong>whales, humans… have a constant body temperature.<\/p>\n

The corresponding a pari<\/em> argument is:<\/p>\n

Both humans and whales are mammals (\u201cbelong to the same genus\u201d, here mammals)
\n<\/em>Humans have a constant body temperature (\u201cwhat is true of a species\u201d, here humans)
\n<\/em>So<\/strong> whales (must) have a constant body temperature (\u201capplies to another spe\u00adcies\u201d, here whales).<\/em><\/p>\n

If the property is not<\/em> generic<\/span>,<\/strong><\/span> then, the conclusion is a paralogism:<\/p>\n

Labradors and poodles are dogs
\nLabradors are gun dogs
\nSo<\/strong>, poodles must be gun dogs.<\/p>\n

The corresponding a pari<\/em> argument is:<\/p>\n

Both Labradors and Poodles are dogs (\u201cbelong to the same genus\u201d <\/em>here dogs<\/em>)
\nLabradors are gun dogs (\u201cwhat is true of a species\u201d, <\/em>here Labradors<\/em>)
\nSo<\/em><\/strong> poodles must be gun dogs (\u201capplies to another species\u201d, <\/em>here gun dogs<\/em>).<\/p>\n

However, poodles are not gun dogs. The property \u201c\u2014 is a gun dog<\/em>\u201d is not a generic property, it belongs to the Labrador as a species, not to the genus \u201cdogs\u201d. Therefore, this characteristic cannot be safely transferred to poodles.<\/p>\n

In short, a trait can be transferred from one species to another species belonging to the same genus only if the trait on which it is based is generic<\/strong>. The validity of the argument depends on the quality of the taxonomy on which it is based, and the argument will be considered persuasive only if people agree on the classification, see the cases below.<\/p>\n

2. The Apparent Deadlocks A Pari<\/em> vs. A Contrario <\/em><\/span>and A Pari<\/em> vs. A Pari<\/em><\/span><\/h2>\n

Two paradoxes are attributed to a pari <\/em>argument. In the same situation:<\/p>\n