The original concept of tithing, in the scriptures, is 10% of the produce OF THE LAND. It is not clear to me if this meant "net produce" (economic rent) or gross produce. The modern concept, at least in most U.S. churches, is radically different: it is 10% of "personal income". "Income" in practice is mostly defined the way the U.S. Congress and its agency, the I.R.S., define it, with most land income omitted and wage and salary income heavily emphasized. Thus, the concept has been turned upside down. Mason Gaffney