Consensus rules allow full nodes (whole nodes) to remain in consensus with other nodes in the network. It is a specific set of rules that all nodes will systematically apply when considering the validity of a block and its transactions. They concern only the validity of blocks and transactions. For example, the Ethereum consensus rules require that blocks only create a certain number of ethers. If a block creates more ethers than allowed, all full nodes will reject this block, even if all other nodes and miners in the world accept it. Adding new consensus rules can usually be done by soft fork, while removing any consensus rules requires a hard fork.