In a soft fork, only previously valid blocks/transactions are made invalid. This means that non-upgraded nodes will still see the transactions as valid and can continue to operate normally, even though they are not aware of potential new rules or features introduced by the updated protocol. Soft forks can be used to introduce new features or make improvements to the existing blockchain without necessitating all participants to update their software. However, to ensure that soft forks are accepted by the network, a majority of the miners must support the new rules; if they do not, the network could face potential splits or confusion.