ABSTRACT
Ancient Romans did not have a god of windows, but Janus was their god of doors, marking the lintels of entrances and gateways with a double-faced image that looked both inwards and outwards. He was a god of time as well as place. The Janus principle is highly relevant to topic of planning history. Planning is by definition an anticipatory activity, addressing events that have yet to occur. To plan means to look ahead and make provision for what the future may hold. Peter Hall never relied upon a single window in researching the future. He pursued methodological pluralism. This chapter begins with one of his most characteristic methods were what we have called the Janus principle, which he called 'historicism'. Lastly, the Janus principle also explains Hall's longstanding interest in the history of utopias—yesterday's imaginary tomorrows.
