Pasch and Peano[edit]The German mathematician Moritz Pasch (1843–1930) was the first to accomplish the task of putting Euclidean geometry on a firm axiomatic footing.[29] In his book, Vorlesungen über neuere Geometrie published in 1882, Pasch laid the foundations of the modern axiomatic method. He originated the concept of primitive notion (which he called Kernbegriffe) and together with the axioms (Kernsätzen) he constructs a formal system which is free from any intuitive influences. According to Pasch, the only place where intuition should play a role is in deciding what the primitive notions and axioms should be. Thus, for Pasch, point is a primitive notion but line (straight line) is not, since we have good intuition about points but no one has ever seen or had experience with an infinite line. The primitive notion that Pasch uses in its place is line segment.
Pasch observed that the ordering of points on a line (or equivalently containment properties of line segments) is not properly resolved by Euclid's axioms; thus, Pasch's theorem, stating that if two line segment containment relations hold then a third one also holds, cannot be proven from Euclid's axioms. The related Pasch's axiom concerns the intersection properties of lines and triangles.
Pasch's work on the foundations set the standard for rigor, not only in geometry but also in the wider context of mathematics. His breakthrough ideas are now so commonplace that it is difficult to remember that they had a single originator. Pasch's work directly influenced many other mathematicians, in particular D. Hilbert and the Italian mathematician Guiseppi Peano (1858–1932). Peano's work, largely a translation of Pasch's treatise into the notation of symbolic logic (which Peano invented), uses the primitive notions of point and betweeness. Peano breaks the empirical tie in the choice of primitive notions and axioms that Pasch required. For Peano, the entire system is purely formal, divorced from any empirical input.