“…The students faced with this concept since their preschool days. When we look at the related literature, there are many studies (Aktaş andAktaş, 2012, Bernabeu, Moreno andLlinares, 2018;De Villiers, 1998;Erez and Yerushalmy 2006;Furinghetti and Paola, 2002, Herbst and others, 2005, Monaghan, 2010Okazaki and Fujita, 2007, Ulusoy, 2015, Ulusoy and Çakıroğlu, 2017 about rectangle with other quadrilaterals but there were no studies which looked for the inclusion relationships by focusing on rectangle while doing this with analyzing them in terms of Van Hiele geometric levels. This study is important with focusing on the thinking levels of students while investigating their definitions in terms of necessity and sufficiency.…”