Why Don't People Use Formal Methods?
Formal methods don't make a lot of sense when the product changes from week to week, or month to month, or even year to year.<p>It seems like the advocates of formal methods assume a waterfall method of software development wherein you develop a spec, formalize it, prove that it works, and then deliver it. That's just not how software works in industry. A lot of it never had formal specs and never will, and whatever specs exist change frequently. By the time a spec is perfected it is out of date and we are already moving on to the next thing.<p>Agile development killed waterfall development and formal methods have not adapted to the agile methodology.