I’ve come to the conclusion that what I value most in architectural work, apart from skill and competence, is conviction. That is why I appreciate the work of Louis Kahn and his teacher Paul Cret equally, because while their work is quite different, it’s executed with a strong sense of purpose. Absent that, architecture risks becoming merely a weak-kneed copy-book reproduction, whether it is modernist or classicist. There is nothing weak-kneed about one of my favorite Philadelphia buildings, the Main Branch of the U.S. Post Office on Market and Thirtieth Street (today it houses the IRS). It was built in 1931-35 and designed by the leading local firm of Rankin & Kellogg. John Hall Rankin was a graduate of MIT and Thomas M. Kellogg had attended MIT and apprenticed with McKim, Mead & White. They formed a partnership in 1891 and acquired a national reputation after winning competitions for several prominent federal buildings. The Post Office, which covers a city block, is a five-story steel frame building clad in Indiana limestone. The flat roof was designed as a landing pad for autogyros that brought air mail from nearby airports in Camden and Philadelphia. The overall composition of the building is Beaux-Arts classicist but the style is Art Deco combined with pre-Columbian Inca motifs. Admittedly an odd combination. I always glance at the granite entrance portal as I walk by. A stylized American eagle is perched above the entrance. The curved Art Deco forms are stylishly streamlined, but they also suggest—mail boxes! The portal contrasts with the smooth limestone wall and the Pre-Columbian patterned panel above. It shouldn’t make sense but it does. That’s conviction.