The chapter deals with Galen’s attack on the pulse-classification of the first-century CE Pneumatist doctor Archigenes, and examines Galen’s reasons for replacing Archigenes’ theory with his own. Galen claims that Archigenes has no idea of the proper method of determining the real species of pulse, and he castigates him for terminological failings as well. But it turns out on close analysis that Archigenes’ actual classification is very close to Galen’s own; and the terminological cavils seem fairly trivial and pedantic. So what is the real substance of Galen’s attack? The chapter suggests that the point at issue is partly simply a matter of professional rivalry, but partly also a consequence of Galen’s insistence on adhering to the properly philosophical method of conducting divisions.