Classes are recognized sets of Units that are grouped according to common properties. Classification intelligence is necessary for organized thinking. Relations are connections between Units of information based on variables or points of contact that apply to them. They are often abstract. Units and Classes are used to build Relations.
Most achievement tests require Relational intelligence.
Systems are more complex than Relations. Systems are organized or structured aggregates of Units of information and are complexes of interrelated or interacting parts. Systems may be made up of Figural, Symbolic, or Semantic content. Transformations are more abstract than Systems. Transformations involve a modification of original information into new information.