Reciprocity Whenever human activities incorporate machines or rigidly prescribed procedures, the modes of human interaction change. In general, technical arrangements reduce or eliminate reciprocity. Reciprocity is some manner of interactive give and take, a genuine communication among interacting parties. Ursula M. Franklin, The Real World of Technology reciprocity
Invisible substance We wanted wood, not only in many visible places, but also in the roof trusses of the homeroom buildings, where they are invisible. Fujita wanted to replace the invisible trusses with steel trusses. They could not understand the idea that it was the actual substance — even though not visible — which would control the feeling of the thing. Christopher Alexander, The Battle for the Life and Beauty of the Earth All the way throughFinished on the inside material