This paper develops a theoretical perspective on AuDHD (autism and ADHD) that moves beyond prevailing models of comorbidity and differential classification. Rather than treating AuDHD as an additive or hybrid category within existing diagnostic systems, it is understood as a boundary case at which the categorical foundations of these systems themselves become unstable. Starting from the observation that AuDHD can neither be consistently typologized nor stably described in functional terms, the paper argues that this instability does not constitute a deficit, but points to a fundamental property of cognition: its non-stabilizability. Cognitive processes are thus not conceived as the processing of stable representations, but as dynamic relations emerging from a structural difference—a “gap”—that cannot, in principle, be fully closed. Within this framework, AuDHD appears as a liminal configuration in which this difference can no longer be smoothed out or functionally subsumed by neuronormative models. This makes visible that existing cognitive and diagnostic frameworks are systematically oriented toward stabilization and, in doing so, exclude precisely those forms of cognition that evade or structurally undermine such stabilization. The paper therefore proposes not to establish AuDHD as a new category, but to understand it as an epistemic boundary case at which the very premises of such categorization become questionable. In this sense, a revision of fundamental assumptions about cognition, identity, and normality becomes necessary. Neurodivergence thus appears not as a variation within a stably conceived system, but as a necessary component of a dynamic cognitive field. This paper is conceived as a supplementary text to the previously published book They Cannot Understand: Why Autism Research Gets It Wrong (DOI: https://doi.org/10.5281/zenodo.19035961) and further elaborates its theoretical premises in the context of the current AuDHD debate. AuDHD is thus not primarily explained, but made visible as a boundary case at which the necessity of stabilizing models itself is called into question.
Timothy Speed (Tue,) studied this question.