Playfair's axiom

E519271

Playfair's axiom is a reformulation of Euclid’s parallel postulate stating that through a point not on a given line there is exactly one line parallel to the given line, fundamental to Euclidean geometry.

All labels observed (7)

How this entity was disambiguated

Statements (46)

Predicate Object
instanceOf geometric axiom ⓘ
parallel postulate formulation ⓘ
assumes existence of at least one line through any two distinct points ⓘ
category axiom of plane geometry ⓘ
clarityAdvantage more intuitive and concise than Euclid's original fifth postulate ⓘ
consequence circles of equal radius are congruent in Euclidean geometry ⓘ
rectangles exist in Euclidean geometry ⓘ
contradictedBy axioms of elliptic geometry ⓘ
axioms of hyperbolic geometry ⓘ
domainOfDiscourse points and lines in a Euclidean plane ⓘ
equivalentTo various other Euclidean parallel axioms ⓘ
expresses uniqueness of parallels through an external point ⓘ
field Euclidean geometry ⓘ
formalization can be expressed in first-order logic over incidence and parallelism relations ⓘ
geometricConsequence angle sum of polygons depends only on number of sides in Euclidean geometry ⓘ
area of a triangle determined by its base and height in Euclidean geometry ⓘ
existence of similar figures of arbitrary size ⓘ
historicalPeriod 18th century formulation ⓘ
implies Pythagorean theorem in Euclidean geometry ⓘ
existence of similar but non-congruent triangles in Euclidean geometry ⓘ
sum of angles in a triangle equals 180 degrees in Euclidean geometry ⓘ
logicalForm uniqueness axiom for parallels ⓘ
logicalStatus equivalent to Euclid's parallel postulate in Euclidean geometry ⓘ
logicalType independent of Euclid's first four postulates ⓘ
namedAfter John Playfair ⓘ
parallelLineCountInEllipticGeometry no parallels through a point not on a given line ⓘ
parallelLineCountInHyperbolicGeometry infinitely many parallels through a point not on a given line ⓘ
quantifierProperty asserts existence and uniqueness of a parallel line ⓘ
reformulationOf Euclid's parallel postulate ⓘ
linked to: Playfair's axiom
relatedConcept Euclid's Elements ⓘ
elliptic geometry ⓘ
hyperbolic geometry ⓘ
non-Euclidean geometry ⓘ
parallel lines ⓘ
requires notion of incidence between points and lines ⓘ
notion of parallel lines ⓘ
roleInTheory distinguishes Euclidean geometry from non-Euclidean geometries ⓘ
states Through a point not on a given line there is exactly one line parallel to the given line ⓘ
teachingUse standard form of the parallel postulate in modern geometry education ⓘ
truthValueInEllipticGeometry false ⓘ
truthValueInEuclideanGeometry true ⓘ
truthValueInHyperbolicGeometry false ⓘ
usedAs modern replacement for Euclid's fifth postulate in many textbooks ⓘ
usedFor characterizing flat (zero curvature) geometric spaces ⓘ
usedIn axiomatic treatments of plane geometry ⓘ
usedWith Euclid's first four postulates ⓘ

How these facts were elicited

Referenced by (8)

Full triples — surface form annotated when it differs from this entity's canonical label.

John Playfair → notableWork → Playfair's axiom ⓘ
Commentary on the Difficulties of Certain Postulates of Euclid → critiques → Euclid's fifth postulate ⓘ
linked to: Playfair's axiom
John Playfair → notableWork → Playfair's axiom ⓘ
subject linked to: Playfair
Playfair's axiom → reformulationOf → Euclid's parallel postulate ⓘ
linked to: Playfair's axiom
John Playfair → notableFor → Playfair’s axiom in geometry ⓘ
subject linked to: John
linked to: Playfair's axiom
John Playfair → hasAxiomNamedAfter → Playfair’s axiom ⓘ
subject linked to: John
linked to: Playfair's axiom
Fifth postulate → alsoKnownAs → parallel postulate ⓘ
subject linked to: Euclid's postulates
linked to: Playfair's axiom
On the Principles of Geometry → mainSubject → Euclid’s parallel postulate ⓘ
linked to: Playfair's axiom