EXCERPT: Christopher Alexander’s forces

Software design patterns were derived from the work of architect Christopher Alexander, specifically his book A Pattern Language: Towns, Buildings, Construction. This excerpt (from episode 39) addresses a problem: most software people don't know one of Alexander's most important ideas, that of "forces".
Sources

• Christopher Alexander et al, A Pattern Language: Towns, Buildings, Construction, 1977.
Mentioned (or that I wish I'd found a way to mention)

• Gamma et al, Design Patterns, 2004
• Eric Evans, Domain-Driven Design, 2003. I also like Joshua Kerievsky's pattern-language-like…