names used in common speech are not always
scientifically accurate, not always the best that could be devised for
the easy acquisition and sure transmission of thorough knowledge. The
plain man's vocabulary, though often twisted aside by such causes
as we have specified, is roughly moulded on the most marked
distinguishing attributes of things. This was practically recognised
by Aristotle when he made one of his modes of definition consist in
something like what we have called verifying the meaning of a name,
ascertaining the attributes that it signifies in common speech or in
the speech of sensible men. This is to ascertain the essence, [Greek:
ousia], or _Substantia_, of things, the most salient attributes that
strike the common eye either at once or after the closer inspection
that comes of long companionship, and form the basis of the ordinary
vocabulary. "Properly speaking," Mansel says,[1] "All Definition is an
inquiry into _Attributes_. Our complex notions of Substances can only
be resolved into various Attributes, with the addition of an unknown
_substratum_: a something to which we are compelled to regard
these attributes as belonging. _Man_, for example, is analysed
into Animality, Rationality, and the something which exhibits these
phenomena. Pursue the analysis and the result is the same. We have a
something corporeal, animated, sensible, rational. An unknown constant
must always be added to complete the integration." This "unknown
constant" was what Locke called the _Real_ Essence, as distinguished
from the _Nominal_ Essence, or complex of attributes. It is upon this
nominal essence, upon divisions of things according to attributes,
that common speech rests, and if it involves many cross-divisions,
this is because the divisions have been made for limited and
conflicting purposes.

[Footnote 1: Aldrich's Compendium, Appendix, Note C. The
reader may be referred to Mansel's Notes A and C for valuable
historical notices of the Predicables and Definition.]

CHAPTER III.

ARISTOTLE'S CATEGORIES.

In deference to tradition a place must be found in every logical
treatise for Aristotle's Categories. No writing of the same length
has exercised a tithe of its influence on human thought. It governed
scholastic thought and expression for many centuries, being from its
shortness and consequent easiness of transcription one of the
few books in every educated man's library. It still regulates the
s