The aim of the author in this essay is to reconstruct the thinking of Thomas Aquinas on the elenctic method used to defend the first principles of Christian theology and the sacra doctrina. Aquinas compares the indemonstrable principles of philosophical sciences with the dogmas of theological science; in effect, neither of the two can be properly proved but instead defended by a confutative approach. Then, an in-depth analysis of the SCG and of the Super De Trin shows that acceptance of the articuli fidei does not depend on apodictic and syllogistic demonstrations, but on probabilistic and persuasive argumentations. While dogmas cannot be syllogistically demonstrated, their bases (the so-called praeambula fidei) are nonetheless completely philosophical, and so they can be proved to anyone solely through reason. Finally, the author underlines the importance in Aquinas of the similitudo as an instrument by means of which theologists are able to validate the reasonability and the plausibility of the indemonstrable principles of faith.
Keywords: Elenchos, theological argumentation, princìpi primi, praeambula fidei, demonstrative reason, persuasive reason