[For example, we may think of the Class "towns," and imagine that we have picked out from it all the towns which possess the Attribute "lit with gas"; and we may thus form the Real Class "towns lit with gas." Here we may regard "Towns" as a _Genus_, "Towns lit with gas" as a _Species_ of Towns, and "lit with gas" as its _Differentia_. If, in the above example, we were to alter "lit with gas" into "paved with gold," we should get the _Imaginary_ Class "towns paved with gold."] A Class, containing only _one_ Member is called an '=Individual=.' [For example, the Class "towns having four million inhabitants," which Class contains only _one_ Member, viz. "London."] pg002½ Hence, any single Thing, which we can name so as to distinguish it from all other Things, may be regarded as a one-Member Class. [Thus "London" may be regarded as the one-Member Class, picked out from the Class "towns," which has, as its Differentia, "having four million inhabitants."] A Class, containing two or more Members, is sometimes regarded as _one single Thing_. When so regarded, it may possess an Adjunct which is _not_ possessed by any Member of it taken separately. [Thus, the Class "The soldiers of the Tenth Regiment," when regarded as _one single Thing_, may possess the Attribute "formed in square," which is _not_ possessed by any Member of it taken separately.] pg003 CHAPTER III. _DIVISION._ § 1. _Introductory._ 'Division' is a Mental Process, in which we think of a certain Class of Things, and imagine that we have divided it into two or more smaller Classes. [Thus, we might think of the Class "books," and imagine that we had divided it into the two smaller Classes "bound books" and "unbound books," or into the three Classes, "books priced at less than a shilling," "shilling-books," "books priced at more than a shilling," or into the twenty-six Classes, "books whose names begin with _A_," "books whose names begin with _B_," &c.] A Class, that has been obtained by a certain Division, is said to be 'codivisional' with every Class obtained by that Division. [Thus, the Class "bound books" is codivisional with each of the two Classes, "bound books" and "unbound books." Similarly, the Battle of Waterloo may be said to have been "contemporary" with every event that happened in 1815.] Hence a Class, obtained by Division, is codivisional with itself. [Thus, the Class "bound books" is codivisional with itself. Similarly, the Battle of Waterloo may be said to have been "contemporary" with itself.] pg003½ § 2. _Dichotomy._