Of all the endeavors to expand the frontiers of knowledge, none has yielded so little to the organizing functions of the human mind as the study of the mind itself. Evidence of misgivings which extend even into the psychological community itself can be found in the usurping of the term "psychology" to denote a physical science committed to the study of objectively observable behavior. It is therefore essential that psychology address itself to a question which is fundamental to its very existence as a science, that is, to what extent and under what conditions can subjective phenomena constitute a valid basis (as data) for a scientific theory.

Although the most apparent shortcoming of psychical data is that it is not accessible to mutual observation for objective verification, it is found that science is actually constructed upon isolated observations of numerically different data presumed to be identical (e.g. the duplication of an experiment). This implies that some factor other than the private nature of psychical observations must be held accountable for the apparent "untrustworthiness" of psychical data. It is discovered that there is a correlation between intraclassification individualization and the evolutionary status of the object or process being observed. This individualization is most apparent in human organisms, and most specifically, in the human psyche. By constructing a phylogeny of psychical functions, much in the manner in which one constructs a phylogeny of living organisms, it is possible to infer the likelihood that a specific psychical function is subject to individual variation (e.g., associations arising from the reasoning process) or, conversely, whether it is likely to be identical irrespective of the particular psyche in which it occurres (e.g.,fear and anger).