In the world of software management there existed a dread place called “dependency hell”. The bigger your system grew and the more packages you integrated into your software, the more likely you were to find yourself, one day, in that pit of despair.
In systems with many dependencies, releasing new package versions used to quickly become a nightmare. If the dependency specifications were too tight, you were in danger of version lock (the inability to upgrade a package without having to release new versions of every dependent package). If dependencies were specified too loosely, you would inevitably be bitten by version promiscuity (assuming compatibility with more future versions than is reasonable). Dependency hell was where you were when version lock and/or version promiscuity prevented you from easily and safely moving your project forward.
As a solution to this problem, Tom Preston-Werner proposed Semantic Versioning, a simple set of rules and requirements that dictated how version numbers are assigned and incremented. Under that scheme, version numbers and the way they changed conveyed meaning about the underlying code and what had been modified from one version to the next. Over the years, SemVer has become the de facto standard for describing software versions in many communities.
Pragmatic Versioning takes up the torch and tries to solve some of the issues that many artifact providers experience when they put SemVer into practice. Instead of defining a completely new versioning system, it is built on top of Semantic Versioning by adding a bit more granularity to the backwards-incompatibility level that can be expressed through a version identifier.