Errata naturae. Cause prime e seconde del mostro biologico tra medioevo ed età moderna

According to one of the most influential definitions, formulated by Michel Foucault in his Les anormaux, the monster is, since the Middle Ages, a violation of a "bio-juridical" order. In critically discussing the historical plausibility of this claim this article explores medical and philosophical conceptions of monsters between medieval and early modern age, addressing in particular the matter of the relationships between first and second causes in nature's errors. The main authors dealt with are Thomas Aquinas, Ambroise Paré, Francisco Toledo and Fortunio Liceti. What emerges is that up to the 17 th century monsters were always conceived as products - and not as real contradictions - of a nature ordered by God's will, goodness and perfection, without a real "bio-juridical" order (as Foucault thinks).