In the begining...or near to it anyways

Charles Spearman (1863-1945)

There is an ongoing controversy as to whether "intelligence" is a unitary (Spearman) or multi-faceted (Gardener).

"...mental abilities of nearly all kinds are positively linked in the sense that if we are good at one thing, we are also likely to be good at others."

Spearman beleived that on average a person's diversity of abilities were intercorrelated, and developed statistical tests to investigate his hypothesis (e.g. Spearmans rho correlations and Factor Analysis).

Ref:

http://www.psych.usyd.edu.au/difference5/scholars/spearman.html

http://nicologic.free.fr/GeneralIntelligence.htm