Blockchains can be permissioned and permission less, Blockchains that require permission limit the parties who can transact on the blockchain and can serve the network by writing new blocks into the chain. A permissioned blockchain determines who may act as transaction validators on their network, such as CGI, MIT and Microsoft. A blockchain developer may choose to make the system of record available for everyone to read but may not wish to allow anyone to be a node, serving the network’s security, transaction verification or mining. With permissioned blockchains, this may or may not involve ‘proof of work’ or some other system requirement from the nodes. Private blockchains with no 'proof of work' (that is, blockchains with no mining) may be not be considered blockchains but simply shared ledgers. There are conflicting views as to the meaning of blockchain.
Let pass through the gates, grant passage to everyone, permits not allowed