John Bogle is either clearly incorrect, or the quotation may be taken out of context and may be unrelated (I don't know); however, the price that the seller sells at is usually not the price that he originally bought at. This difference, specifically the change in dollar value for the same object being sold, is how capital enters and leaves that system. Note that this is specifically about money-capital, and not capital based on other resources -- so if Bogle was talking about some other kind of value, he could easily be correct; although from that quotation alone, it really looks like he's talking about stock-trading money, and even values the market at $24T, so... I'm guessing he just didn't think it all the way through.