premise: Budapest consists of two parts, Buda and Pest, which are situated on opposite sides of the river and connected by a series of bridges.
hypothesis: Buda and Pest function as separate cities.
reason: We don't know that this is true.  It's possible, but they are part of the same city and connected to each other, so there is not reason to think they function any differently than 2 adjacent neighborhoods in any other city.