A soft fork refers to a blockchain fork that occurs when the rules for validating the blockchain are made more stringent. In contrast
, a hard fork refers to a blockchain fork that occurs when the validation rules are relaxed.
In the case of a hard fork, programs that do not adopt the new validation rules are highly likely to reject blocks and transactions created under the new rules as invalid. This creates a discrepancy in the determination of the blockchain fork between programs that adopt the new rules and those that do not, posing the risk that the fork will become permanent.
In contrast, with a soft fork, blocks and transactions created under the new validation rules are considered valid, even if they were created using the old validation rules.
Therefore, assuming that a majority of miners and validation programs adopt the new validation rules, the risk of a permanent fork is reduced, and it becomes possible to converge onto the branch with the new validation rules in the future, thereby building a stable blockchain.
