The concepts and discoveries of modern neuroscience now challenge many of the presumptions that influence diagnostic decisions within neurology, psychiatry, and clinical neuropsychology. Many of these presumptions are derived from archaic bivariate models such as the mind-body argument, organic-functional dichotomy, and single lesion-single behaviour causality. Thirteen basic principles which may be useful for inferring more reliable and accurate relationships between microstructural function an clinical manifestations are developed.