Our position that determinations of dimensionality are, in part, a function of whether putative dimensions play different roles in relation to other psychological processes is based on the usefulness of distinctions for psychological theory and clinical application. When two constructs have been shown to be distinct, in the sense that they appear to play different roles in relation to other psychological processes, then researchers and clinicians will typically benefit by distinguishing between them. When they have not been shown to be distinct in this way, then there is neither a practical benefit of doing so nor a theoretical necessity to do so. As William James put it, “There can be no difference anywhere that doesn't make a difference elsewhere—no difference in abstract truth that doesn't express itself in a difference in concrete fact” (as cited in McDermott, 1967, p. 379).
