Prime Matter Is Three-Dimensionality. The Debate on the Extension of Prime Matter from Zabarella to Galileo

Aristotle had left his pupils with a conundrum to solve: the nature of prime matter. Throughout the centuries, this concept remained the most obscure and elusive in Aristotle’s philosophy. While there were a number of conflicting opinions about the nature of prime matter, the debate was revived at the end of the sixteenth century when the logician and natural philosopher Jacopo Zabarella (1533–1589) proposed to identify prime matter as a material body of indefinite extension (quantitas interminata) that is bound within precise limits and shapes by the intervention of the actualising form (forma substantialis). Zabarella’s solution was further refined by his colleagues, including the theologian Paolo Sarpi (1557–1623), the physicians Girolamo Fabrici da Acquapendente (1533–1618) and Santorio Santori (1561–1636) and eventually by Galileo Galilei (1564–1642). They turned prime matter into a quantifiable substratum and developed some early forms of corpuscularianism or atomism. My aim in this paper is to recapture the essence of these developments starting from Zabarella’s own formulation of the problem of the extension of prime matter. In the second part, I will analyse its impact on the natural philosophies of Sarpi, Santorio, and Galileo, showing how the debate on prime matter constituted the background against which early forms of quantified experimentation emerged.