From the scholastic point of view, sacraments are signs which can thus be subject to semiotic theories, but these, however, can conflict with traditional ideas of the nature and the efficacy of the sacraments. Based on commentaries on Peter Lombard’s Sentences, Ueli Zahnd studies this conflict between assertions by authorities on theology and philosophical insights of logic, physics and metaphysics in the late Middle Ages. The author focuses on as yet scarcely studied authors of the 15th and early 16th centuries whose various ways of dealing with the problem of the sacraments and the interaction between philosophy and theology enables an analysis of this little known scholastic eraallowing established interpretations, such as the split between nominalists and realists, to be questioned.