The two-factor theory: did Spearman under-admit the group factors between g and s?

Charles Spearman, answered from the texts and cited to the page.

The position in brief

In its first form the theory held that each ability is the sum of the one general factor and a factor specific to that single task — a clean dichotomy, g and s, with no faculties in between.1234

Sources

  1. In a similar manner, we may get for any other abilities, c, d, etc., Mor = To9- 8a ap os, +Sozy Mex = Veg +S + Tes, + Sexy For any other individual y, there ensues analogously: May = Yag-8y + Vasq- Say) Moy = Vo9-8y + Tos,-Soyy These varied applications of the formula (17) are given in order to illustrate the following points.
    The Abilities of Man, p. 431
  2. The definite establishment of this claim will be attempted in Part IT. PROPOSED EXPLANATIONS OF G PsycHotocicat Basis. Aim of present Chapter. Interpretation as " Intelligence." Recourse to Attention or Will. Hypothesis of " Mental Energy." Depreciatory Views. PHYSIOLOGICAL Basis. Energy. Plasticity. The Blood. Various. Possrp1tiry oF CoMpLex BasIs. Early Regard Paid to this Point. Impossibility in General.
    The Abilities of Man, pp. 87–88
  3. In general, it seems quite as good as, if not better than, that usually reached in determining the mechanical equivalent of heat and thus establishing the law of conservation of physical energy. UNIVERSALITY OF G REQUIRED GENERAL SURVEY OF COGNITION. Use of Fundamental Laws. The Apprehension of One's Own Ex- perience. The Eduction of Relations. The Eduction of Correlates. DETECTION OF G WITH ALL TEN RELATIONS.
    The Abilities of Man, p. 161
  4. At one extreme lay the talent for classics, where the ratio of the influence of g to that of s was rated to be as much as 15 tox. At the other extreme was the talent for music, where the ratio was only 1 to 4." Here at once we have before us the essence of the whole doctrine, the seedling from which all else has sprung.
    The Abilities of Man, pp. 75–76

Where the argument is made

  • The original two-factor theory — every performance is g plus a task-specific s, with nothing between

How the argument was received

The clean dichotomy did not survive the evidence, and I did not pretend it did: I came to admit GROUP factors — abilities broader than one task yet narrower than g. That admission was mine, made as the data required it, and it turned the two-factor theory into the ancestor of the hierarchical view rather than its rival.