Twenty years have now elapsed since Professor Thurstone’s ingenuity pulled the factor problem out of its tetrad difference quagmire. Most of us have watched Thurstone’s brain-child grow. One might say that the fledgling was so precocious as to reach maturity during the first ten years of its life. Its development was fostered not only by Thurstone but also by the resistance it encountered. Indeed, even as an infant, it was forced to throw aside its swaddling clothes in order to kick back at the Spearmans, the Tryons, the Anastasis, and others who sometimes rightly, ofttimes wrongly, pointed a finger at supposed imperfections. The youngster weathered more or less successfully the many storms it had stirred up, and by the end of its tenth year of life had in the hands of Thurstone made significant contributions and was ready for the sober coming-of-age evaluation of its strengths and weaknesses by Dael Wolfle. We suspect that the facts of life pointed out by Wolfle had already been whispered to the growing adolescent by none other than Thurstone himself.