The Power of Four is a sweeping history of four foundational concepts that have guided Western thought from the earliest days of Western civilization.

Divided into four sections, the book takes an evolutionary stance, looking at how each concept—elements, humors, temperaments, and types—developed and then evolved into the next. It also leans heavily on the archetypal nature or "power" of four, both "fourness," as in four elements, humors, and temperaments, and "fourfoldness," as in 4 x 4 or 16 personality types.

Although touching upon other numerological schemes related to personality theory, the author stays focused on “the power of four,” the most prevalent construction upon which most of Western thought is built.