'Private' just means 'limited'. We are still talking about multiple distinct counterparties transacting with each other. Public blockchains replace the need fo

'Private' just means 'limited'. We are still talking about multiple distinct counterparties transacting with each other. Public blockchains replace the need for trust with, essentially, energy usage. That's what gets you your validity, despite operating in a hostile environment. They give you a shared, single source of truth about the state of whatever system you've embodied on that blockchain. The problem they are solving is the undesirability (or impossibility) of trusting an intermediary. Private blockchains replace the need for reconciliation between parties who minimally trust* one another with a method for provably ensuring everybody has and will get the same information. They also give you a shared, single source of truth about the state of your particular market, but you get that in an environment where parties on the network are assumed to be behaving well. The problem these solve is the cost and complexity in establishing a trusted third party. It isn't hard technically to have a reliable ledger, but it is hard structurally and operationally. The point of a private blockchain is to mutualize the infrastructure required to form that single source of truth. You could do it with a trusted intermediary operating a big shared database, but you'd have to set one up in a market where that doesn't exist and assign to them complete responsibility for your record keeping. Private blockchains are a way for parties with a shared problem - the cost of reconciling their independent books - to construct a solution that doesn't require forming and staffing some new industry utility, or abrogating control over their own records (so they can maintain secrecy of trade data, for example.) *I mean by this, they have stronger economic and legal incentives to cooperate in doing business with each other than they do in ripping off the other guy. Put another way, their horizon for trusting a counterparty extends beyond the immediate transaction on the table at any given moment. This isn't the case in anonymous individual peer-to-peer transactions.