I am fully aware of the differences between equal temperament and what might be called the "natural scale." I've been all through that, from Pythagoras' experiments and findings with "monochords" (discovering that the relationships between musical notes is not just arbitrary, there is a mathematical basis for such relationships—"The Physics of Music," Cornish School, 1963—) to the eventual development of equal temperament and the salutary affect this had on the music that followed its adoption.

What I was calling into question was the statement that the third of the triad is "out of key." It is very slightly "out"—of tune—in relation to an overtone of the root note, but it is not "out of key." A musical instrument which is perfectly tuned—not tuned to equal temperament—is playable, "in tune," in only one key. The further away one gets from that key around the circle of fifths, the further out of tune the instrument is. With equal temperment, a couple of notes in each key are very slightly out of tune (most people's ears don't even notice it), but it can be played in all keys.

The terminology I use (regarding such things as what constitutes a chord and what does not) is standard among formally trained musicians. Since I did study music in academic settings, I tend to use the language that is commonly used in music schools and conservatories all over the United States and Europe, and that is used by trained musicians everywhere who play music in what may be called the "Western tradition" (stemming from European music). I find that this terminology works perfectly well in reference to British Isles and American folk music as well. It is a common language among musicians.

"Common usage" may eventually change the meaning of the word "chord." But I doubt it very seriously. When dealing with the complexities of, say, classical symphonic music, musicians need to know what their colleagues are talking about, so they try to be fairly precise. And the established terminology has worked quite well for a few centuries now.

I find that it is self-taught musicians who tend to cavil at this terminology and often wish to redefine it in their own terms, and this can lead to lack of precision, difficulty in attempting to communicate specific information, and general confusion.

I'm all for clear communication, and I think it's a good idea if people know the meaning of the words they use so other people know what they are talking about and they know what other people are talking about. If everyone makes up his or her own definitions, especially for technical terms, we wind up with a musical Tower of Babel.

I fully realize that I'm tilting at windmills here.

Just for kicks, pull up Google and, in the search box, type "chord" and "definition" and see what you get.

Don Firth

P. S. And by the way, there is no rule or law in music theory that says you can't or shouldn't use dyads. The bone of contention here is what you call it. If you call it a "chord," someone who knows a bit of music theory is going to assume that it contains a 3rd. One could refer to it as, say, "an A chord with a missing 3rd." That may seem like a lot of verbiage, but classically trained musicians are using modifiers all the time:   "a first-inversion C major," which means a C major chord with the E (3rd) in the bass rather than the root. Folk musicians do that. Case in point:   "E7" which is an E major chord with a D (minor seventh interval above the root) added.