The attributes of a term may be separated into three classes: differentia, property and accident. It would appear possible, therefore, to define a term by enumerating the accidents only or by enumerating the properties, or, finally, by stating the differentiae. But if the enumeration is confined to accidents the chances are that the statement will be a description, not a definition, as accidents are seldom sufficiently characteristic to determine the boundaries of a term. This leaves open two distinct ways of defining a term: First, by naming the properties or properties and accidents only; second, by stating the differentiæ only. The former kind is the so-called descriptive definition, while the latter is the logical. (2) _A descriptive definition of a term is a description of its nature by means of its properties and accidents._ (3) _A logical definition of a term is a description of its nature by means of its differentiæ._ THE THREE KINDS OF DEFINITIONS ILLUSTRATED AND COMPARED. Etymological Definition of Trigon. A trigon is a figure of three corners. Descriptive: A trigon is a figure which has three sides and three angles, the sum of the latter being equal to two right angles. Logical: A trigon is a polygon of three angles. It is seen that an etymological definition is simply a root-word analysis. In the case of _trigon_, the prefix comes from the Greek, meaning three, while the root-word comes from the Greek meaning corner. The descriptive definition of trigon names the properties, “three sides and three angles” (differentiæ) and the accident, “the sum of the angles of which equals two right angles.” The logical definition of trigon simply states the proximate genus, “polygon,” and the differentia, “three angles.” =6. WHEN THE THREE KINDS OF DEFINITIONS ARE SERVICEABLE.= The etymological definition is helpful in furnishing a cue for remembering the descriptive and logical definitions. It also leads to precision of expression――the right word in the right place. Here is where the knowledge of a foreign language, particularly Latin, is helpful. The descriptive definition is best adapted to the child-mind. Children think in the large; are not given to hair-splitting discriminations, and, therefore, _many_ characteristic marks must be mentioned in order to insure a mastery of the content. With children the logical definition is often too brief to be clear. For example, it is easy to see which of the following definitions would be better adapted to the child-mind. _Logical_: A square is an equilateral rectangle. _Descriptive_: A square is a figure of four equal sides and four right angles. The logical definition may be introduced to the student of the secondary school.