The two studies conducted by Weiss, Keith, Zhu, and Chen in 2013 on the Wechsler Adult Intelligence Scale (WAIS-IV) and the Wechsler Intelligence Scale for Children (WISC-IV), respectively, provide strong evidence for the validity of a four-factor solution corresponding to the current hierarchical model of both scales. These analyses support the calculation of the four index scores and the Full Scale IQ. In this article, we discuss some limits of these validation efforts: (a) the incomplete measurement of the construct, (b) the problem of correspondence between factors and broad abilities, (c) the gap between a structural model and a functional model of intelligence, and (d) the difficulty of combining the measurement of global intelligence and broad abilities. Finally, the option of a five-factor model underlying the index scores is analyzed and its potential for future Wechsler scales is discussed. (Contains 3 tables.)