Mental operations have been investigated at a developmental level by Jean Piaget, and from a psychometric perspective by J. P. Guilford.

[3] J. P. Guilford's Structure of Intellect model described up to 180 different intellectual abilities organized along three dimensions—Operations, Content, and Products.

SI theory comprises multiple intellectual abilities organized along three dimensions—Operations, Content, and Products.

The SI model includes six products, in increasing complexity: Therefore, according to Guilford there are 6 x 5 x 6 = 180 intellectual abilities or factors.

Each ability stands for a particular operation in a particular content area and results in a specific product, such as Comprehension of Figural Units or Evaluation of Semantic Implications.