When filing an IFR flight plan, the language of FAR 91.169 makes listing an alternate airport the default: You have to name one unless the circumstances of the flight are such that it falls under both of the two listed exceptions: First, the airport must have a published instrument approach procedure. Second, the forecast weather meets the 1-2-3 rule: For an hour before to an hour after the ETA at your destination, the weather is forecast to be equal to or better than a 2000-foot ceiling with three statute miles’ visibility.
Interestingly enough, a surprising number of instrument pilots and instructors forget the part about an instrument approach being required at the destination to avoid filing an alternate. Even if the wx is going to be clear and a million for the next three days, if your destination doesn’t have a published approach, you’ve got to list an alternate airport on your flight plan.
Oh—and the FAA caught on to the gamesmanship pilots used for decades with shorter-range airplanes, which involves filing the true destination as the alternate and listing an airport on the way as the destination. In 2005, the FAA proclaimed such a procedure was careless and reckless, and let it be known that pilots who ran short (or out) of fuel when doing so could face a certificate action.