This monograph argues that the structuralist movement in linguistics was curtailed prematurely, before its contribution to cognitive science could be fully realized. Building upon Roman Jakobson's pioneering work on the nature of the linguistic sign, a new and detailed appreciation of the role of sign relations in the ultimate structuring of consciousness is presented, proving that the structural approach has as much to contribute today as any current cognitive theory. This study takes the view that the structure which linguistic signs themselves evince should be treated as an organic property of mind in its own right, as the device by which the ultimate differences in meaning in the human cognitive sphere are realized. Adherence to this principle assumes not only that the linguistic sign must be fundamentally monosemic, but also that the level of abstraction at which the relations between signs function must lie beyond the logical or rational level where polysemy is the rule. The study demonstrates that while the conceptual relations or categories uncovered at such a higher-order level of consciousness are of necessity highly abstract and hidden from normal awareness, they are nevertheless neither ineffable nor devoid of content. Rather, the categories identified and defined in this study are shown to have verifiable correlates at the supra-rational level where transpersonal rather than ego-oriented psychology operates, the level that Jung termed the collective unconscious. It is here that we find corresponding properties in reports from altered states of consciousness, in the structure of myths worldwide, as well as in studies of the image-making capacity of the human mind. Ultimately, when the structure of actual linguistic signs is treated as an ordered set of conceptual relations, one necessarily arrives at the conclusion that the sign relations of different languages are anything but Whorfian, but are all pointing to the same universal set of conceptual properties. This set of properties is then shown to be able to account for the relations between signs in all areas of linguistic structure, from the grammatical to the lexical and the syntactic. The monograph goes on to provide a detailed account of the process of making reference, of how speakers are able to contextualize the truly abstract conceptual relations inherent in the structure of signs in their language, to produce a potentially infinite variety of polysemous meanings in actual speech situations at whatever level of concreteness they choose; and how the feedback from such acts of communication determines the evolutionary trajectory of a system of signs conceived as a living organism, specifically as a neuronal structure inherent in the human brain operating as a fundamentally probabilistic or stochastic system.