Well, Republic and Democracy give +1 commerce to all tiles producing at least 1 commerce. That can be quite a boost. And despotism/anarchy take 1 commerce away from a tile that's producing at least 2. You'll always get at least 1 commerce from a roaded tile.
yes i understand.you say republic and democracy gives no exact bonus only makes the things easier for changing science slider.
i knew the commerce bonus that comes from those governments.also sorry for asking the game specifics you probably bored about this.people still asking something about something from civ3 while civ4 is preparing to be in stores.