THE REAL ERROR OF CYRIL BURT 333
group factors existed, Brown and Stephenson (1933) gave twenty-
two cognitive tests to three hundred ten-year-old boys. They cal-
culated some disturbingly high tetrads and dropped two tests
"because 20 is a sufficiently large number for our present pur-
pose." They then eliminated another for the large tetrads that it
generated, excusing themselves by stating: "at worst it is no sin to
omit one test from a battery of so many." More high values
prompted the further excision of all tetrads including the correla-
tion between two of the nineteen remaining tests, since "the mean
of all tetrads involving this correlation is more than 5 times the
probable error." Finally, with about one-fourth of the tetrads gone,
the remaining eleven thousand formed a distribution close enough
to normal. Spearman's "theory of two factors," they proclaimed,
"satisfactorily passes the test of experience." "There is in the proof
the foundation and development of a scientific experimental psy-
chology; and, although we would be modest, to that extent it con-
stitutes a 'Copernican revolution' " (Brown and Stephenson, 1933,
P- 353)-
For Cyril Burt, the group factors, although real and impor-
tant in vocational guidance, were subsidiary to a dominant and
innate g.
For Thurstone, the old group factors became primary mental
abilities. They were the irreducible mental entities; g was a delu-
sion.
Copernicus's heliocentric theory can be viewed as a purely
mathematical hypothesis, offering a simpler representation for the
same astronomical data that Ptolemy had explained by putting the
earth at the center of things. Indeed, Copernicus's cautious and
practical supporters, including the author of the preface to De
Revolutionibus, urged just such a pragmatic course in a world pop-
ulated with inquisitions and indices of forbidden books. But Cop-
ernicus's theory eventually produced a furor when its supporters,
led by Galileo, insisted upon viewing it as a statement about the real
organization of the heavens, not merely as a simpler numerical
representation of planetary motion.
So it was with the Spearman-Burt vs. the Thurstone school of
factor analysis. Their mathematical representations were equiva-
lent and equally worthy of support. The debate reached a fury of
intensity because the two mathematical schools advanced radically