Quality is not something to be "proved". You can make arguments, demonstrations and provide evidence that the quality of something is higher than the general run of similar things, or higher than something else, but quality is a multi-faceted concept that has too many thing going into it to say things like "this has 5.7 more quality units than that, plus or minus 1.37." That's just a bit silly.

This doesn't mean that the concept is meaningless, even though marketing hype has made its meaning harder to find. Many things we value can't be adequately quantified along one, two or seven dimentions.

• "I enjoyed that {meal|music|tenmis game|user interface}."
• "That's an elegant {proof|vase|algorighm}."
• "That {argument|expanation|alibi} makes a lot of sense."

There are some very useful and informative things that can be said to support these statements about complex things, and some things that can be usefully quantified as well, but it's a mistake to think you can boil it all down to something provable, just as it is a mistake to suppose that just because something can't be proved there is no meaning to be found in it and nothing worthwhile there.

After all, the completeness of Mathematics and the effectivness of proof in Mathematics can not be proved, but Mathematics is still pretty useful.

So, what are useful guides to quality? What have people found to be good early indicators that they will later think of a piece of code as

• performing well,
• easy to learn and/or use, and
• easy to maintain?

Albannach and eyepopslikeamosquito have given us a start, and I'm interested in hearing what others have found useful

If it were so simple that ISO 9000 could give us the answer, we wouldn't have enlightening discussions, now would we.