Hundreds of bitcoin supporters have tweeted attacks at me for arguing that bitcoin is not real money. But historically, money must be a reliable medium of exchange, and a reliable store of value. Bitcoin meets neither of these definitions.

How can you transact using so-called digital money when prices fluctuate by hundreds of dollars in the space of an hour, or less? You might think you bought something for $500. But by the time the retailer processes payment, the so-called digital-currency price drops to $100.

Both buyers and sellers lose big because bitcoin is not a reliable medium of exchange with a dependable store of value. It is backed by nothing but pure speculation. You can’t even hedge it, because there’s no interest rate. You can barely even get a price quote — not for the value of the product being bought or sold, but for the value of the monetary medium of exchange.