(5) The Kinds of Definitions. (1) Etymological. (2) Descriptive. (3) Logical. THREE KINDS ILLUSTRATED AND COMPARED. (6) When the Three Kinds are Serviceable. (7) The Rules of Logical Definition. (1) _Essentials._ (2) Same _size_. (3) Do not _repeat_. (4) _Unambiguous._ (5) _Language_ affirmative. (8) Terms Which Cannot be Defined Logically. Summum genus. Infima species. Sui generis. Collective terms. A single attribute. =11. SUMMARY.= (1) To be logical one must acquire the habit of accurate definition. This topic ought to appeal strongly to the school teacher, who should above all others make his work stand for clearness, pointedness and continuity. (2) A predicable is a term which can be affirmed or predicated of any subject. The five predicables are Genus, Species, Differentia, Property and Accident. (1) A Genus is a term which stands for two or more subordinate classes. (2) A Species is a term which represents one of the subordinate classes. The _proximate genus_ of a species is the next class above the species, while the _summum genus_ is the highest possible class in any graded series of terms. The lowest class is the _infima species_ of that series. The lowest class may be individual. In natural history genus and species are not relative terms, but absolute, having a fixed place in the series of gradations. The term genus possesses a double meaning: it may be used to represent objects (extensionally) or qualities (intensionally). (3) The differentia is that attribute which distinguishes a given species from all the other species of the genus. (4) A property of a term is any attribute which helps to make that term what it is. Differentia is a property according to definition. Some logicians would not include the differentia in the content of the term property. (5) An accident of a term is any attribute which does not help to make it what it is. Some authorities divide accidents into separable and inseparable. (3) A definition of a term is a statement of its meaning by enumerating its characteristic attributes. (4) Definitions explain a term intensionally, while logical division explains a term extensionally. (5) There are three kinds of definitions: (1) etymological, (2) descriptive, (3) logical. An etymological definition is based upon the derivation of the term; a descriptive definition states the characteristic properties and accidents of a term, while a logical definition is simply a statement of the differentia of a term. (6) The etymological definition leads to precision of expression, the descriptive definition is best adapted to the child-mind, while the logical definition belongs to the realm of secondary education.