Editing Leonhard Euler (section)

===Logic===
Euler is credited with using [[closed curve]]s to illustrate [[syllogism|syllogistic]] reasoning (1768). These diagrams have become known as [[Euler diagram]]s.<ref name=logic/>
[[File:Euler Diagram.svg|thumb|upright|An Euler diagram]]

An Euler diagram is a [[diagram]]matic means of representing [[Set (mathematics)|sets]] and their relationships. Euler diagrams consist of simple closed curves (usually circles) in the plane that depict [[Set (mathematics)|sets]]. Each Euler curve divides the plane into two regions or "zones": the interior, which symbolically represents the [[element (mathematics)|elements]] of the set, and the exterior, which represents all elements that are not members of the set. The sizes or shapes of the curves are not important; the significance of the diagram is in how they overlap. The spatial relationships between the regions bounded by each curve (overlap, containment or neither) corresponds to set-theoretic relationships ([[intersection (set theory)|intersection]], [[subset]], and [[Disjoint sets|disjointness]]). Curves whose interior zones do not intersect represent [[disjoint sets]]. Two curves whose interior zones intersect represent sets that have common elements; the zone inside both curves represents the set of elements common to both sets (the [[intersection (set theory)|intersection]] of the sets). A curve that is contained completely within the interior zone of another represents a [[subset]] of it.

Euler diagrams (and their refinement to [[Venn diagram]]s) were incorporated as part of instruction in [[set theory]] as part of the [[new math]] movement in the 1960s.<ref name=lemanski/> Since then, they have come into wide use as a way of visualizing combinations of characteristics.<ref name=rodgers/>