The Tree of Knowledge (ToK) System is a theoretical approach to the unification of psychology developed by Gregg Henriques, associate professor and Director of the Combined-Integrated Doctoral Program in Clinical and School Psychology at James Madison University.
The outline of the system was published in 2003 in Review of General Psychology. Two special issues of the Journal of Clinical Psychology in December 2004 and January 2005 were devoted to the elaboration and evaluation of the model. The latest evaluation of this model appeared in a December 2008 special issue of Theory & Psychology''.
The Official Website on the Tree of Knowledge System claims that the ToK is
...a new unified theory of knowledge that maps the pieces of the scientific puzzle in a novel way that connects Quantum Mechanics to Sociological processes and everything in between into a coherent whole. The most novel aspect of the ToK is its visuo-spatial depiction of knowledge as consisting of four dimensions of complexity (Matter, Life, Mind, and Culture) that correspond to the behavior of four classes of objects (material objects, organisms, animals, and humans), and four classes of science (physical, biological, psychological, and social).