Professionals use specs to invite others to participate in the work.
One kind of spec outlines the solution. In clear language, it defines the work to be done. A good solution spec defines an outcome with no room for error or variety. “It’s this. Not that, not that, but this. If it’s this, we’re done.”
The other kind of spec outlines the problem. It invites team members to innovate on the way to producing a solution. “If it solves this problem within these constraints, we’re done.”
Neither effective spec approach involves “I’ll know it when I see it.” A spec eliminates mindreading and guesswork.