167. At each step in the descent from the term at the top, which is
called the 'Summum genus,' to the individual, we decrease the
extension by increasing the intension. Thus by adding on to the bare
notion of a thing the idea of independent existence, we descend to the
term 'substance,' This process is known as Determination, or
Specialisation.

168. Again, by withdrawing our attention from the individual
characteristics of a particular sheep, and fixing it upon those which
are common to it with other animals of the same kind, we arrive at the
common term, 'sheep.' Here we have increased the extension by
decreasing the intension. This process is known as Generalisation.

169. Generalisation implies abstraction, but we may have abstraction
without generalisation.

170. The following example is useful, as illustrating to the eye how
a decrease of extension is accompanied by an increase of intension. At
each step of the descent here we visibly tack on a fresh
attribute. [Footnote: This example is borrowed from Professor Jevons.]

Ship
|
Steam-ship
|
Screw steam-ship
|
Iron screw steam-ship
|