Triplets vs. not-triplets

This is a pretty fine point of theory, but it comes up a lot on this site, so I want to state my thinking about it, so I can link to it every time it comes up, and keep any lurking pedants off my back. People for whom music theory is a social weapon and not a practical tool. You know the type.

Basically, I'm freer in my use of the word triplet than are many other people with a college education. I want to explain what's up with that, and clarify some things about this whole area of rhythm and meter.

So, a definition: 

A triplet is a rhythm of three notes played in the space of two notes of the same value. For example, an 8th note triplet is three 8ths played in the space of two 8ths, indicated by that numeral 3 written above the notes. In music theory class, that and only that is correctly called a triplet. It has to be artificial to the time signature; a temporary three note subdivision in a piece written with mainly a standard, straight-8th, two-note subdivision.

Three-note subdivision of the beat: triplets

With compound meters (most meters with an 8 in the bottom number), a three-note/ternary subdivision is implied. It's native to the meter, so the rhythm above notated in 6/8 would not be triplets:

Also a three-note subdivision of the beat: not triplets

Those are just 8th notes. If I say 8th notes and the meter is 6/8, it means those triplet-looking things that sound exactly like triplets. Which is confusing to some people, because they are often not real comfortable with compound meters; in their mind 8th notes = those march-sounding 1&2&3&4& things, and these triplet-sounding 8th notes in 6/8 seem to be an entirely different creature.


Where I get into terminology trouble: 

Because I teach and write, I need to talk about individual beats and partial beats of this rhythm often, and the easiest, shortest, most understandable word for that is triplet. So I say triplet in that context. Middle note of the triplet. Last two notes of the triplet. In some contexts it's easier for the students' understanding to say it that way.

Yes, that really is the entire point of this post. Sometimes I say triplet to talk about a single beat of rhythm with a three note subdivision even if it isn't really a real triplet. I also often say triplet feel— which just refers to anything in music that sounds like triplets, whether it “is” triplets or not.

It's actually not a hard and fast thing that terminology must be consistent with the meter of the piece. Jazz-educated musicians may say (or a chart may indicate) triplet feel, 6/8 feel or 12/8 feel regardless of the written meter, and people are always clarifying points of rhythm using terms of a different meter. Latin musicians refer to the 3 side of clave as the tresillo— which means triplet; another example. Even in written music, if a piece in 4/4 has a lot of running triplets in it, the copyist may stop putting the numeral 3 over every single beat, and make a notation that the continuing rhythm is still triplets, effectively changing the meter to 12/8.

It doesn't matter. The point is, practical musical communication is often not correct to the letter as defined by music theory. There is usually more than one correct answer for describing a piece of rhythm, and often different terms are necessary to describe it to different people in different contexts.