The five phases
Ken Wilber's oeuvre can be divided into five phases:
Phase 1 (1977-1979), which he himself characterizes as his "romantic-Jungian" phase. Like many romantic philosophers and Jungian psychologists, he sees spiritual growth as a (complete or partial) return to a condition which existed in the past, but which has been lost during the process of growing up, c.q. cultural history.
Phase 2 (1980-1982), in which he shifts to developmental psychology as larger context to integrate Eastern and Western psychology. Spiritual growth he now sees as something that comes after growing up. In other words, we have not lost God, we grow into Him, by a gradual process of development.
Phase 3 (1983-1987), in which he refines his model of development over the years. Development is no longer understood as a homogenous proces, in which the self passes through a number of stages respectively, but as a complex process, consisting of several lines of development (cognitive, emotional, social, spiritual, etcetera) and the self somehow has to maintain a delicate balance between these lines.
In the years 1987-1995 he does not publish much, due to personal circumstances, primarily because his wife gets ill and dies in 1989.This period is chronicled in the book Grace and Grit in 1991.
Phase 4 (1995-2001), in which he adds a socio-cultural dimension to his model of individual development, and gives more attention to neurological processes that are involved in consciousness. With his image of the four quadrants (intentional, neurological, cultural and socio-economic) he demonstrates the interdependency of these dimensions, and the onesidedness of views that base themselves on only one quadrant, and doubt the validity of the other quadrants.
Phase 5 (2001-present), called "post-metaphysical", in which Wilber shifts his focus from a metaphysical background philosophy (involution/evolution, levels of being) to an evolutionary view based on Sheldrake's notion of the "Presence of the Past" in all four quadrants. He retains a few basic tenets of the perennial philosophy (the One, some involutionary givens), but sides with this-worldly views of human evolution, as exemplified in Spiral Dynamics. His model encompasses All Quadrants, All Levels, All Lines, All States, All Types -- or in shorthand: AQAL.