According to Charles Jencks, the following are some themes of "Postmodern Architecture": expression hybrid, Variable space brimming with surprises, Semiotic articulation, eclecticism Depending on the environment, a variable blended aesthetic; expression of content and semantic appropriateness towards function, Pro-organic and applied ornamentation (structure, etc.) Postmodern architects often borrow from various sources, including traditional styles, popular culture, and modern designs. They also play with perspective, showing that what is seen depends on where you stand or look. Often considered a part of Modernism, Postmodern architecture developed in the 1970s and 1980s. It is characterized by its use of materials such as glass, concrete, metal, and plastic instead of stone or wood. The emphasis is on functionality rather than decoration. The aim is to create comfortable, economical buildings suitable for today's world market. Modernists rejected all tradition in design, whereas Postmodernists believe that history is important for understanding how certain concepts can be adapted to different situations. For example, Postmodern architects have used historical styles such as Renaissance and Baroque to create new buildings suited to modern life. They have also taken ideas from ancient cultures and incorporated them into their work. For example, Louis Khan uses Mayan and Egyptian motifs in his buildings to illustrate the relationship between past and present generations. He believes this shows that modern designers should not ignore history when creating new works of art.