The notion of force generalizes the kinds of criteria that software engineers use to justify designs and implementations. For example, in the classic study of algorithms in computer science, the main force to be resolved is efficiency (time complexity). However, patterns deal with the larger, harder-to-measure, and conflicting sets of goals and constraints encountered in the development of every artifact you ever create. For example:

What is force resolution?

Alexander's descriptions of patterns includes the idea that a pattern should represent a kind of equilibrium of forces. (Even Alexander has been criticized (even by himself) for not always carrying this out in a convincing manner.) This is the same notion as optimality as seen for example in the analysis of algorithms in computer science, but applied to the kinds of harder-to-measure forces described in the previous question.

It is usually impossible to analytically ``prove'' that a solution optimally resolves forces. (In fact, it is hard to define the notion of ``proof'' here, or even to see what use such a proof would have.) On the other hand, it is all too easy to come up with ``just-so'' stories that provide wrong or deceptive rationales for solutions. Even the most concientious pattern authors sometimes don't fully understand why a solution works as well as it does, or appreciate its full range of applicability.

For these reasons, the patterns community expects that arguments be backed up with: