Line Postulate:Thereis exactlyone line throughany two points.Similarly, thereis exactlyone planethat containsany threenon-collinearpoints.To illustratethis, ask three
friendsto hold up the tips of their pencils,and try and lay a pieceof paperon top of them.If your friendsline
up their pencils(makingthe pointscollinear),thereare an infinitenumberof possibleplanes.If one hand
movesout of line, however, thereis only one planethat will containall threepoints.The followingimage
showsfive planespassingthroughthreecollinearpoints.
PlanePostulate:Thereis exactlyone planethat containsany threenon-collinearpoints.If two coplanarpointsform a line, that line is also withinthe sameplane.
Postulate:A line connectingpointsin a planealso lies withinthe plane.