In scholastic

logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...

, differentia is one of the

predicables Predicable (Lat. praedicabilis, that which may be stated or affirmed, sometimes called ''quinque voces'' or ''five words'') is, in scholastic logic, a term applied to a classification of the possible relations in which a predicate may stand to its ...

. It is that part of a

definition A definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories: intensional definitions (which try to give the sense of a term), and extensional definitio ...

which is predicable in a given

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

only of the

definiendum A definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories: intensional definitions (which try to give the sense of a term), and extensional definitio ...

; or the corresponding " metaphysical part" of the object.

Origin

Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...

implicitly employed the concept of differentia when he conceived his method of ''diairesis''.

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...

was the first to use the term ''diaphora'' (διαφορά) in a systematic fashion; but he had no explicit theory about it, and his understanding of the term is controversial. A theory was only provided by Porphyry's explicit treatment of the

presented in his ''

Isagoge The ''Isagoge'' ( el, Εἰσαγωγή, ''Eisagōgḗ''; ) or "Introduction" to Aristotle's "Categories", written by Porphyry in Greek and translated into Latin by Boethius, was the standard textbook on logic for at least a millennium after his ...

''. The elaborate scholastic theory of the predicables evolved οn the basis of Boethius' translation of the Isagoge, where the Greek term ''diaphora'' was rendered in Latin as "differentia". In ancient Greek ''

adiaphora Adiaphoron (; plural: adiaphora; from the Greek (pl. ), meaning "not different or differentiable") is the negation of ''diaphora'', "difference". In Cynicism, adiaphora represents indifference to the s of life. In Pyrrhonism, it indicates things ...

'' - is the negation of ''diaphora'' - is an important term in

Hellenistic philosophy Hellenistic philosophy is a time-frame for Western philosophy and Ancient Greek philosophy corresponding to the Hellenistic period. It is purely external and encompasses disparate intellectual content. There is no single philosophical school or cu ...

. However, only in

Pyrrhonism Pyrrhonism is a school of philosophical skepticism founded by Pyrrho in the fourth century BCE. It is best known through the surviving works of Sextus Empiricus, writing in the late second century or early third century CE. History Pyrrho of E ...

does it appear to be a denial of Aristotle's notion of diaphora.

Logical meaning

In the original, logical sense, a differentia is a concept — the notion of "differentia" is a second-order concept, or a "second intention", in the scholastic nomenclature. In the scholastic theory it is a kind of essential predicate — a predicate that belongs to its subjects ''de re'' necessarily. It is distinguished against the

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

by expressing the (specific) essence of the object only partially and against the ''genus'' by expressing the determining rather than the determined part of the essence.

Ontological meaning

Although the primary meaning of "differentia" is logical or second-order, it may under certain assumptions have an ontological, first-order application. If it is assumed that the structuring of an essence into "determining" and "determinable" metaphysical parts (which corresponding to a differentia and a genus respectively) exists in reality independently of its being conceived, one can apply the notion "differentia" also to the determining metaphysical part itself, and not just to the concept that expresses it. This is common in

Scotism Scotism is the philosophical school and theological system named after John Duns Scotus, a 13th-century Scottish philosopher-theologian. The word comes from the name of its originator, whose ''Opus Oxoniense'' was one of the most important ...

, where the metaphysical parts are said to be formally distinct. If, on the other hand, any mind-independent structuring on the part of the essence is denied (like in

Thomism Thomism is the philosophical and theological school that arose as a legacy of the work and thought of Thomas Aquinas (1225–1274), the Dominican philosopher, theologian, and Doctor of the Church. In philosophy, Aquinas' disputed questions a ...

or Suárezianism), then the partitioning of the essence into a generic and a differentiating part must be considered as merely "conceptua", whereas the actual realities corresponding to the differentia and to the genus evade as really the same. These assumptions therefore do not permit any ontological application of the notion of differentia.

Origin

Logical meaning

Ontological meaning

See also