Bitcoin is fiat, it's not backed by anything of real value and doesn't have a government or a strong (and I mean national-government-kind strong) player behind it that is willing to devote actual resources to prop it up (which is what all other fiat monies have and which is why they usually stay around for a century or so, after that they either become obsolete or their value greatly diminishes due to inflation). It has all of the Aristotelian properties of money (durable, portable, fungible), and some extra ones too, except intrinsic value. So it's not money according to Aristotle. When a better system comes along (and it would be trivially easy for that to eventuate, imagine, e.g. China or a major corporation or - even better - an industry association offering an altcoin backed by gold, agricultural land, shares, face time with celebrities, mentoring time - hey these are good ones! etc.), the value of bitcoins will go to zero as everybody will want the new, better altcoin that has at least some intrinsic value. The same death spiral cannot happen in the case of government-backed fiats when a new fiat is introduced, for a number of reasons. Bitcoin is inertia-backed fiat. I'll take the government-backed variety any time.