\
SENSIBLE || INSENSIBLE
||
ANIMAL
/ \
RATIONAL || IRRATIONAL
||
MAN
//||\\
// || \\
// || \\
// || \\
// || \\
// || \\
// || \\
_Socrates_ _Plato_ _Aristotle_

Beginning with 'Substance,' as _summum genus_, and adding the
difference 'Corporeal,' we frame the species 'Body.' Taking 'Body' as
the genus and adding the difference 'Animate,' we frame the species
'Living Body;' and so on till 'Man' is reached; which, being _infima
species_, is only subdivisible into individuals. But the division of Man
into individuals involves a change of principle; it is a division of the
denotation, not an increase of the connotation as in the earlier steps.
Only one side of each dichotomy is followed out in the 'tree': if the
other side had been taken, Incorporeal Substance would be 'Spirit';
which might be similarly subdivided.

Genus and species, then, have a double relation. In denotation the genus
includes the species; in connotation the species includes the genus.
Hence the doctrine that by increasing the connotation of a name we
decrease its denotation: if, for example, to the definition of 'lion' we
add 'inhabiting Africa,' Asiatic lions are no longer denoted by it. On
the other hand, if we use a name to denote objects that it did not
formerly apply to, some of the connotation must be dropped: if, for
example, the name 'lion' be used to include 'pumas,' the tufted tail and
mane can no longer be part of the meaning of the word; since pumas have
not these properties.

This doctrine is logically or formally true, but it may not always be
true in fact. It is logically true; because wherever we add to the
connotation of a name, it is possible that some things to which it
formerly applied are now excluded from its denotation, though we may not
know of any such things. Still, as a matter of fact, an object may be
discovered to have a property previously unknown, and this property may
be fundamental and co-extensive with the denotation of its name, or even
more widely prevalent. The discovery that the whale is a mammal did not
limit the class 'whale'; nor did the discovery that lions, dogs, wo