Share 'How to determine par?'

I want to hear others' thoughts on this subject to help prove to someone esle what par should be on a given hole. This such person claims that a Par 3 doesn't have to be reachable for a putt at birdie (assume an "average" amateur playing from the am pads or the "average" pro from the pro pads). Well....I asked how then, are you supposed to birdie that Par 3??? (my opinion is that if a hole isn't…