We have described numerous novel concepts so far and it is time now to discuss how consensus is achieved. In the Tangle, new incoming messages do approve several existing messages, and in such a way every message is approved by an increasing number of other messages. Every message is issued by a node that carries some consensus mana. In this way, every node builds up an approval weight, or the sum of the consensus mana of the node approving this message. Using this approach, honest messages (or those that follow the protocol) are approved very quickly and efficiently.
However, in some situations, nodes have to decide whether a given message should be considered for being part of the Tangle. For instance, in the case of a double spend, every node has to decide which of the conflicting messages it has to approve. To ensure that every node takes the same opinion on a given message nodes use our new consensus protocol, the Fast Probabilistic Consensus (FPC).