Representative of the hierarchical theories are Cattell (1971), Carroll (1993) and Horn (1994). They describe hierarchies moving from the specific—e.g., spelling ability and speed of reasoning in the Carroll model—to the general—G in the Cattell and Carroll models. While G is too general for current purposes, it is not clear whether all or most of the abilities found at the opposite end of the hierarchy (i.e., specific abilities) would fit our definition of life skills as being necessary for success in life. For the current purpose, the most relevant and useful abilities included in these models are found somewhere in the middle.

Two "middle-level" abilities common to most hierarchical models are crystallized abilities (also referred to as Gc) and fluid abilities (also referred to as Gf). Carroll describes crystallized abilities as the accumulated knowledge base, including language development, verbal and printed language, comprehension, and lexical knowledge. Similarly, Horn defines crystallized abilities, or acculturation knowledge, as

"…measured in tasks indicating breadth and depth of the knowledge of concepts and forms of reasoning that have been developed by humans over the course of many centuries and passed on from one generation to the next. Gc can be thought of as the intelligence of the culture that is incorporated by individuals through a process of acculturation"(p. 443).

Carroll's description of fluid abilities centers on reasoning abilities, namely, general sequential reasoning, inductive reasoning, and quantitative reasoning. Horn defines fluid abilities as measured in tasks requiring inductive, deductive, conjunctive, and disjunctive reasoning to arrive at an understanding of relations among stimuli, to comprehend implications, and to draw inferences (p. 443).

The ALL framework assumes that these two abilities, crystallized and fluid, are essential to a model of life skills for several reasons. First, it is easy to conceive that acquisition of them in some way or another is necessary for success in life. Second, they appear distinct—an important quality as many of the skills and abilities uncovered in the search for life skills are similar or overlapping. Whereas tests of fluid ability primarily measure the results of current information-processing skills (reasoning), tests of crystallized ability, in contrast, primarily measure the result of previously applied information-processing skills (comprehension). In addition, although measures of the two abilities may show some statistical correlation, the number of studies separating them as distinct factors (Carroll, 1993) is so large that there seems to be little argument for their relative, although not total, independence. Finally, the two abilities show different patterns of growth and decline with age (Horn, 1994). Fluid ability tends to increase from infancy onward until the late 20s or early 30s and then to start a period of usually gradual decline. Crystallized ability tends to increase until rather late in life and only then begins to show some decline.

Other abilities frequently appear in psychometric theories. Most prominent among them is spatial visualization (Gv), an ability associated with spatial problem-solving (Horn, 1976). While one must keep these other abilities in mind, of the abilities found in psychometric models, crystallized and fluid abilities are the most distinct and widely accepted, and, thus, present the most compelling case for inclusion as distinct components of the ALL life skills framework.