Bruno follows Plato's Phaedrus in distinguishing four kinds of divine madness: prophetic, ritual, poetic, and erotic. All four involve a transport beyond ordinary rational control — a possession by a power greater than the individual. The heroic frenzy is the highest form of the erotic: not desire for any finite object but the soul's passionate recognition of its own infinite ground and its restless movement toward it. The heroic philosopher is distinguished from the merely amorous poet by the universality of his object: he is in love not with a particular beauty but with Beauty itself.
Bruno develops the paradox of the heroic frenzy through the metaphor of the hunt: the philosopher pursues an object he can never capture. The divine beauty that is his true object is infinite; each finite glimpse of it — each philosophical insight, each moment of mystical contact — is real but incomplete. The hunter becomes the hunted: in pursuing the infinite, the philosopher is seized by it, transformed by the encounter, made more infinite himself. This is not frustration but the proper mode of the philosopher's relationship to its object.
The highest phase of the heroic frenzy involves a kind of blindness — the philosopher's ordinary cognitive faculties are overwhelmed by the direct encounter with the infinite. Bruno develops the Actaeon myth: the hunter who sees the naked Diana and is transformed into a stag, destroyed by his own hounds. The philosopher who glimpses the infinite directly cannot contain what he has seen within normal cognitive categories; he is "blinded" in the sense that finite objects no longer satisfy, and yet the blindness is a form of higher vision. It is the coincidence of opposites applied to knowledge itself.
On the Heroic Frenzies (De gli eroici furori) was published in London in 1585, dedicated to Philip Sidney. It combines lyric poetry (sonnets) with philosophical commentary, making it the most literary of Bruno's Italian dialogues.