a system of classes designed to represent the mental disorders according to a fixed rule

The ordering of classes in a hierarchy, according to their similarities and differences. A class ordered lower in the hierarchy is said to inherit the structure and behaviour of the class(es) above it.

The grading of particles too small to be screened in accordance with their size, shape, and density by control of their settling rate through a fluid medium (water, slurry, or air).

is a method of sizing fine particles by exploiting differences in settling velocity in water or air.

Separation of a powder into fractions according to particle size.