t's Philosophy of the Mind, part i, chapt. iv. sect. iii. p. 99.]

13. ABSTRACT GENERAL IDEAS NECESSARY, ACCORDING TO LOCKE.--To give
the reader a yet clearer view of the nature of abstract ideas,
and the uses they are thought necessary to, I shall add one more
passage out of the Essay on Human Understanding, (IV. vii. 9) which is as
follows: "ABSTRACT IDEAS are not so obvious or easy to children or the
yet unexercised mind as particular ones. If they seem so to grown men it
is only because by constant and familiar use they are made so. For, when
we nicely reflect upon them, we shall find that general ideas are
fictions and contrivances of the mind, that carry difficulty with them,
and do not so easily offer themselves as we are apt to imagine. For
example, does it not require some pains and skill to form the general
idea of a triangle (which is yet none of the most abstract,
comprehensive, and difficult); for it must be neither oblique nor
rectangle, neither equilateral, equicrural, nor scalenon, but ALL AND
NONE of these at once? In effect, it is something imperfect that cannot
exist, an idea wherein some parts of several different and INCONSISTENT
ideas are put together. It is true the mind in this imperfect state has
need of such ideas, and makes all the haste to them it can, for the
CONVENIENCY OF COMMUNICATION AND ENLARGEMENT OF KNOWLEDGE, to both which
it is naturally very much inclined. But yet one has reason to suspect
such ideas are marks of our imperfection. At least this is enough to show
that the most abstract and general ideas are not those that the mind is
first and most easily acquainted with, nor such as its earliest knowledge
is conversant about."--If any man has the faculty of framing in his mind
such an idea of a triangle as is here described, it is in vain to pretend
to dispute him out of it, nor would I go about it. All I desire is that
the reader would fully and certainly inform himself whether he has such
an idea or no. And this, methinks, can be no hard task for anyone to
perform. What more easy than for anyone to look a little into his own
thoughts, and there try whether he has, or can attain to have, an idea
that shall correspond with the description that is here given of the
general idea of a triangle, which is NEITHER OBLIQUE NOR RECTANGLE,
EQUILATERAL, EQUICRURAL NOR SCALENON, BUT ALL AND NONE OF THESE AT ONCE?

14. BUT THEY ARE NOT NECESSARY FOR COMMUNICATIOPN.--Much is here
said of the di