Does Not Knowing Justify the Taking?

Comments from a blogger on my recent post " Moment of Truth" got me thinking and the reason for this latest post.The blogger said, if they knew the source of the money then you do the right thing and return it to the rightful owner,if not why return?.Hmmm...so hypothetically speaking, say on one Monday evening,after a long gruelling day at work on your way home, you fight your way thro' the crowded subway and manage to get into the train before it slams shut on your face. You find this one seat still available and thanking your lucky stars you plonk down on the seat to find a bag under your feet,curiously opening the bag...i know!! i know!!Put aside your neo post 9/11 phobia of unattended packages for a minute!!!....you open the bag and find unaccounted money in the bag.Then do you take the money as gift from above or do you try to find the rightful owner and give it back?... It happens to me all the time, I mean, not finding a bag of money, but while walking on the crowded Manhattan streets with my friends. My friends usually ask me step aside, so they can pick up the $20 bill I was standing on!!! They simply follow the adage of "Finders Keepers". So does that mean it's o.k. to keep the smaller bills, but if larger sum then handover to proper authorities?. But large or small it is the concept that matters right?.How do we justify it? Does our necessity justifies the taking?. or not knowing who it belongs to?.