Contrary to common belief, Lavoisier's greatest phlogistic rival was not Joseph Priestley but Richard Kirwan, a fact that was firmly recognized by both the Lavoisians as well as Priestley himself. During the 1780s, which saw the unprecedented rise of the chemistry of air(s), Kirwan's 'ingenious modifications...into the theory of phlogiston', in Mme. Lavoisier's words, became the most dominant alternative to the revisionist pneumatic interpretations of the French. A genealogical contextualization of Kirwan's phlogistic contributions, the circumstances of their emergence and the nature of their evolution and impact, reveals the intricate process of transformation that pneumatic phlogistic thought and practice have undergone during the final years of phlogiston's existence. Originally introduced as an adverse reaction to Scheele's phlogistic reasoning, Kirwan's work evolved as a sophisticated integration between notions of aerial permutations and Adair Crawford's innovative formulation of the phlogistic role of heat, with its origins in the Scottish pneumatic tradition of Black and Irvine. Examining Kirwan's views against the background of metaphysical conflicts over the constitution of pneumatic entities and the role of phlogiston in pneumatic processes traces their origins and advances to a complex interplay between innovation and renovation, proclamation and reclamation, thus depicting the dynamics of (dis-)continuity in the broader phlogistic sphere from which Kirwan's 'modifications' have stemmed and which they came to forcefully represent.