Spearman found that if a person got a high (or low) score on one kind of test, he probably (but not always) would get a similar score on the other kinds of tests. Because of this, he said that a person's intelligence could be described with one number. He called this number "g" (for general factor). Tests that use abstract reasoning are usually the best to tell what the scores on the other kinds of tests probably will be. Because of that, Spearman thought that a person's abstract reasoning ability (how good he was at solving puzzles or problems) was what other kinds of intelligence are based on.