Secondly, according to Goldhagen, Kahn strove for "an architecture of authenticity." Authenticity is a concept popularized by the existentialist writer Jean-Paul Sartre, who, in Goldhagen's words, believed that "To live authentically, one has to strive for a heightened awareness not only of oneself but also of one's place in a specific historical moment and place. This requires acute perception of one's social and physical environment, which is difficult because a person tends to apprehend the objects and buildings that surround her as instruments". Authenticity encourages people to focus "not on the instrumentality of the everyday world but rather on an object's shape, texture, and materiality." In contrast to other modern architects like Mies van der Rohe, Kahn shunned "the diaphanous and the transparent so that he could press the viewer up against materiality, substance and weight." Goldhagen notes that "It is all but impossible to enter one of Kahn's buildings and not to notice it, not to inspect it or look intently at it." Kahn strove for an aesthetic of authenticity at First Unitarian, says Goldhagen, by designing with a blunt honesty of materials and by laying bare the process of construction. Kahn said, "I believe in frank architecture. A building is a struggle, not a miracle, and the architect should acknowledge this."
