Descartes’ technical projects, agendas and senses of identity shifted over time, entangled and displayed great successes and deep failures, as he morphed from a mathematically competent, Jesuit trained graduate in neo-Scholastic Aristotelianism to aspiring prophet of a systematised corpuscular-mechanism, passing through stages of being a committed , advocate of a putative ‘universal mathematics’, and projector of a grand methodological dream. In all three dimensions—projects, agendas and identity concerns—the young Descartes struggled and contended, with himself and with real or virtual peers and competitors, hence the title ‘ ’.