(1) That the boundary lines between
such groups are absolutely arbitrary, a matter of definition only; and
(2) that the individuals comprising one of the groups do not make up a
homogeneous type.

Nevertheless, since terms like the above are convenient and will
probably continue to be used, it is desirable to give them as much
definiteness as possible. On the basis of the tests we have made,
including many cases of all grades of intelligence, the following
suggestions are offered for the classification of intelligence
quotients:--

_I Q_ _Classification_

Above 140 "Near" genius or genius.
120-140 Very superior intelligence.
110-120 Superior intelligence.
90-110 Normal, or average, intelligence.
80- 90 Dullness, rarely classifiable as feeble-mindedness.
70- 80 Border-line deficiency, sometimes classifiable as
dullness, often as feeble-mindedness.
Below 70 Definite feeble-mindedness.

Of the feeble-minded, those between 50 and 70 I Q include most of the
morons (high, middle, and low), those between 20 or 25 and 50 are
ordinarily to be classed as imbeciles, and those below 20 or 25 as
idiots. According to this classification the adult idiot would range up
to about 3-year intelligence as the limit, the adult imbecile would have
a mental level between 3 and 7 years, and the adult moron would range
from about 7-year to 11-year intelligence.

It should be added, however, that the classification of I Q's for the
various sub-grades of feeble-mindedness is not very secure, for the
reason that the exact curves of mental growth have not been worked out
for such grades. As far as the public schools are concerned this does
not greatly matter, as they never enroll idiots and very rarely even the
high-grade imbecile. School defectives are practically all of the moron
and border-line grades, and these it is important teachers should be
able to recognize. The following discussions and illustrative cases will
perhaps give a fairly definite idea of the significance of various
grades of intelligence.[28]

[28] The clinical descriptions to be given are not complete and are
designed merely to aid the examiner in understanding the significance of
intelligence quotients found.

FEEBLE-MINDEDNESS (RARELY ABOVE 75 I Q.) There are innumerable grades of
mental deficiency ranging from somewhat below average intelligence to
profound idioc