Hi Don,

You're quite right: A 3rd isn't "out of key". It's a limitation on my part to express the concept of "vals" in the English language. In English the term is attached to the "key", which in turn is associated with a scale. The 3rds are indeed in a scale, in equal temperament tuning.

Having said that, such 3rds don't accord well with the 1st. The reason is that equal temperament tuning gives a 5th, very close to just tuning, at the cost of a 3rd that is quite far from just tuning. The character that we hear is the lack of accord. I'm not saying it's a bad thing; as so often it's imperfection that make out world colourful. But it does explain why including a 3rd can be good, while stressing it can be less so.

The word "accord" I used above on purpose, of course, since that's where the word "chord" stems from.
Oxford: group of notes sounded usu. together, combined according to some system. [orig. cord f. ACCORD]
Webster: a combination of tones that blend harmoniously when sounded together [Middle English cord, short for accord]

Since I have little formal training in music, I have to go with what I learned since I started looking into this fascinating field at age six or seven. So while the facts might be that there is a professional definition for chord and that a good book on music theory wouldn't tell me anything new, we ought to remember that a professional definition is only intended for use within the profession's theoretical field. Unless those educated to use it form majority of those in the applied field, and they chose to use it there as well, such a term should be qualified. So, while I'm not going to argue that there may be a different "music theoretical definition" of "chord", that doesn't change the ordinary meaning indicated above.

BFN
                                                                Mysha

P.S.
While I was writing that, I thought up an example of the alternative: Mathematically a group need not actually include any members, which would allow me to argue, based on the above, that a group of no notes form a chord (the according I'll prove by pointing out that there's no discord in the group). I'm not going to apply that to music theory, though, simply because to most a group indicates at least two members. (-:

                                                                Mysha