In modern times the so?called consequentia mirabilis (if not-P, then P). then P) was first enthusiastically applied and commented upon by Cardano (1570) and Clavius (1574). Of later passages where it occurs Saccheri?s use (1697) has drawn a good deal of attention. It is less known that about the middle of the 17th century this remarkable mode of arguing became the subject of an interesting debate, in which the Belgian mathematician Andreas Tacquet and Christiaan Huygens were the main representatives of (...) opposite views concerning its probative force. In this article the several phases and moves of that debate are delineated. (shrink)

Seventeenth century scholastics had a rich debate about the ontological status and nature of lacks, negations, and privations. Realists in this debate posit irreducible negative entities responsible for the non-existence of positive entities. One of the first scholastics to develop a realist position on negative entities was Thomas Compton Carleton. In this paper I explain Carleton's theory of negative entities, including what it is for something to be negative, how negative entities are individuated, whether they are abstract or concrete, and (...) how they affect their subjects. I argue that for Carleton, negative entities are conceived as spatially extended simples that affect their subjects by means of spatial overlap. I also show how Carleton responds to some theological worries about his realism concerning negative entities. (shrink)