Louis I. Kahn is cleary one of 20th century great architects. The character of his philosophy of architecture can be condensed as simple words; Architectural Essence, because the very nature of his work based on historicity is so fundamental. Some contemporary architects and architectural critics regard it as a symbol of Post-Modern Architecture era expressing relative multiplicity or an expression of Heideggerian existentialism, but others do as the attribute of fundamentalist like absolute Plato's Idea. Comparing the former, studies of the latter theme have been executed superficially and somewhat biasedly for last decades. In the context, this paper attempt to reanalyze Kahn's idea of ‘Architectural Essence’ with the deep view of Platonist focused on the concept of binary opposition and causality.