Soft fork

In plain words

A soft fork tightens Bitcoin's rules without breaking old software. Blocks that pass the new rules still pass the old, so nodes that never upgrade keep working on the same chain. This is how Bitcoin improves itself — SegWit (2017) and Taproot (2021) shipped this way. The catch: old nodes cannot check the new rules, so real upgrades still want most of the network on board.

Why it matters

• Upgrades that force no one's hand and split no coin.
• The trick is tightening-only: rules may be added compatibly, never loosened.
• Every major upgrade since 2017 has been one.

Not to be confused with

• Hard fork — loosens or changes rules so old software rejects new blocks. Different animal.

Go deeper

• Hard fork
• SegWit
• Taproot