ABSTRACT
No human investigation can be called real science if it cannot be demonstrated mathematically. This chapter focuses on that part of the theory which asserts that intelligence is the general or all-round cognitive ability which mediates success in such tests whatever their nature. Charles Spearman has called this "the indifference of the indicator"; in other words, if a test or test item fulfils the conditions for a "good" test or test item laid down in his laws of neogenesis, then it should not matter much which item or test was chosen for the measurement. The chapter explains the logical basis of factor analysis with a minimum of mathematics. A basic understanding of what the factor analyst is trying to accomplish, and how he sets about it, will suffice for the purpose of seeing whether the Plato-Spencer-Spearman theory is viable, whether it must be rejected, or whether it has to be supplemented in some way or other.
