The nature of "being" has also been debated and explored in Islamic philosophy, notably by Ibn Sina (Avicenna), Suhrawardi, and Mulla Sadra. A modern linguistic approach which notices that Persian language has exceptionally developed two kinds of "is"es, i.e. "ast" ("is", as a copula) and "hast" (as an existential "is") examines the linguistic properties of the two lexemes in the first place, then evaluates how the statements made by other languages with regard to "being" can stand the test of Persian frame of reference.