Gregg Henriques is an American psychologist. He is a professor for the Combined-Integrated Doctoral Program, at James Madison University, in Harrisonburg, Virginia, US. He developed the "Unified Theory Of Knowledge" (UTOK), which consists of 8 key ideas that Henriques claims results in a much more unified vision of science, psychology and philosophy. The first key idea and most central is called the Tree of Knowledge (ToK) System, which provides a new map of cosmic evolution and the way science functions as a justification system that empirically maps behavioral complexity and change. Central to the argument for the ToK System is what Henriques calls, "the problem of psychology" which refers to the fact that the field of psychology has resided in a pre-paradigmatic state and lacked a clear definition and subject matter since it was founded in the later part of the 19th Century. Henriques first published the outline of his work in 2003 in Review of General Psychology in the paper, The Tree of Knowledge System and the theoretical unification of psychology. Two special issues of the Journal of Clinical Psychology in 2004 and 2005 were devoted to the elaboration and evaluation of the model, as was a special section in Theory and Psychology in 2008. In 2011, he published A New Unified Theory of Psychology and later that year he started his popular blog on Psychology Today called Theory of Knowledge: A Unified Approach to Psychology and Philosophy.