 The logical theory of the Contributions is quite primitive, but the work nonetheless contains a number of important insights. Following Aristotle, Bolzano distinguished two sorts of proofs: those that aim merely to convince us that something is the case and those which also show why it is so. He called the former “certifications” (Bolzano 2004b: 254: “confirmations”) [Gewissmachungen], the latter “groundings” [Begründungen]. The concept of grounding reflects the “objective connection among truths”, which need not and usually does not coincide with the subjective order of recognition. It would later become the fundamental concept in Bolzano’s treatment of axiomatic theories in the TS.