During their time in office, British governments’ styles of political judgement or bias in policymaking often become shorter in term and less intellectually coherent, sometimes in passive or coping ways, sometimes shifting toward imposition. This article offers an explanation, developing the neo-Durkheimian theory of institutional dynamics. Changing judgement style, it argues, is driven by changes in administrations’ informal institutional ordering of social organisation. “Isolation dynamics” are shifts in that ordering towards weakly cohesive but strongly constrained “isolate” forms. Increased isolate ordering is reflected in less cohesive but more constrained judgement style. Novel distinctions within isolate ordering explain key differences among administrations’ trajectories. Using extensive archival data, three British administrations between 1959 and 1974 are compared. The study finds that, among otherwise contrasting administrations, reinforcement or undermining in informal social organisation drove changes in styles of political judgement, as shown in their ways of framing policy problems, risks, time horizons, etc.

The increasing appreciation of structural plasticity, namely the capacity of the nervous system to alter not only its function but also its constitution in response to changing conditions, indicates a profound transformation in the scientific comprehension of the human brain. The research on adult neurogenesis, i.e. on the de novo formation of neurons in the mature brain, has been chosen as a circumscribed field to study the controversies that accompany the transition from the concept of a stable to that of a structurally plastic mammalian brain. Building on the concepts of thought style and thought collective developed by Ludwik Fleck, this article investigates the ways in which neurogenesis in the adult brain has changed from being negated to being accepted and highly valued, and consequently has become the focus of a novel research field. This analysis covers a period from the second half of the twentieth century up to the present. The development of research on adult neurogenesis has been shaped by two opposing views: the understanding of a particularly immutable and thus specifically human brain on the one hand, and a plastic brain which remains malleable during the entire adult life, on the other hand. This plastic human brain has created new space for the articulation of the ‘therapeutic promise’, since it lends itself much more readily to therapeutic intervention than a stable brain: the article argues this to be decisive in promoting the transformation of thought style within the neurosciences.