 He worked particularly on the borderline between mathematics and philosophy, motivated by the problem of distinguishing logical calculi from general calculi. He supported David Hilbert’s foundational program having led to metamathematics and proof theory, but focused on language and semantics. Language is necessary to present logical systems. He suggests a formalized language with a degree of exactness even exceeding the exactness of mathematical languages. He calls this language “Leibniz language” L (cf. Scholz 1944). Leibniz languages are symbolic languages with exactly defined means of expression. Each expression is a finite string of characters using a given symbolism according to well-determined rules. If the means of expression are restricted in such a way that (1) these expressions always have sense, and (2) it is decidable whether the produced expressions are true in all possible worlds (universally valid, allgemeingültig), then L is called a “Universal Leibniz Language”. A universally valid fundamental expression is called a Leibniz Theorem. A logic calculus is defined as a set of truths presentable by a Leibniz theorem over L.