490 EVENING DISCOURSES 
In occupational analysis much has been done to determine the require- 
ments for success in different occupations. But a vast field still awaits 
investigation, while much of what has been done is sadly defective from the 
psychological standpoint. Such matters as courses of training, prospects, 
seasonal fluctuations, hours of work and wages have been satisfactorily 
enough treated by those who have been engaged in occupational analysis. 
But information is still lacking as to the precise physical and mental 
abilities and qualities of temperament and character which are likely to 
favour success in different industrial, commercial and professional occu- 
pations. When they have been described, they are usually couched in such 
vague or identical terms that, as has been justly said, they ‘ are scarcely more 
illuminating than the remarks commonly made by centenarians when 
invited to explain the secret of longevity.’ Consequently we are very far 
from being able to classify occupations and processes in such a way that 
a person who possesses the abilities and qualities required for success in 
one member of a group of occupations may reasonably be expected to 
succeed in any other member of the same group, and to fail in other groups 
of occupations. It is obvious that the analysis and classification of occupa- 
tions requires the skill of the trained psychologist ; he has already started 
on this work. 
He began it by assessing the general intelligence required for success in 
different levels of occupational life. He chose general intelligence both 
because of its importance and because he possesses already a sufficiently 
reliable means of estimating it. Important as it is that a young person does 
not enter an occupation which needs higher intelligence than he may 
possess, it is equally important that he does not enter an occupation of so 
routine a nature that it makes insufficient demand on the intelligence which 
he may possess. Excessive boredom must be avoided as much as excessive 
strain. The result of much psychological research has been to establish 
the working hypothesis that a certain single factor of general ability runs 
through all mental and manual work—the ability to discern relevant relations 
and to make appropriate use of them. This innate ability to discern 
relevant relations and to make appropriate use of them may be usefully 
called ‘ general intelligence.’ Mathematically we may isolate it, but in 
practice it cannot be separated from the material on which it works. For 
this reason tests have had to be devised for assessing abstract or linguistic 
intelligence and other tests for assessing practical or concrete intelligence. 
In the former we employ ‘ verbal’ tests, tests involving symbols—the use 
of words, numbers and abstract ideas ; in the latter we employ ‘ perform- 
ance ’ tests, involving the manipulation of concrete objects. 
I throw now on the screen, first, examples of a widely used verbal test of 
intelligence and, next, examples taken from a battery of performance tests 
of intelligence. These tests have been devised to estimate, so far as possible, 
innate intelligence as distinguished from acquired or examination knowledge 
which, owing to lack of interest, illness, etc., on the one hand, or owing to 
‘cramming’ on the other, may not yield a true index of intelligence. 
Repeated researches have definitely proved the greater reliability of intelli- 
gence tests than examination marks in the assessment of intelligence. As 
I have stated, no intelligence test evokes general intelligence and nothing 
more: indeed no psychological test can be devised which involves the play 
of only one mental factor ; there is besides intelligence a ‘ verbal factor’ 
involved in carrying out a verbal intelligence test ; and there is similarly 
a ‘ practical factor ’ involved in carrying out a practical intelligence test. 
1 A. Macrae, Talents and Temperaments, 1932, p. 148. 
