I am a beginner to western classical music. In Howard Goodall's The Story of Music, he mentions “Triads are the chords around which every harmonic, or chordal, journey is structured, in virtually all the Western music written between the early fifteenth century and our own time”. What does he mean by that?. Even Leonard Bernstein on his analysis of "Eroica" says that triads are basis of classical music. What difference did triad make to western music?
Well, to address what Howard Goodall meant by this, I'd just read what he says on the next couple pages. Goodall actually isn't really talking about triads per se here; he's oversimplifying the history quite a bit.
What's he's really talking about at this time in music (fifteenth century, with Dunstaple and Dufay) is the recognition of thirds and sixths as true consonances. In notated Western music of the fourteenth century and earlier, thirds and sixths were not treated in composition as consonant intervals that felt like "resolutions" or stable places of rest. Instead, when they occurred as part of vertical harmony, they would ultimately need to resolve to somewhere else (generally an octave or perfect fifth, eventually).
The fifteenth century saw the rise of so-called tertian harmony, which allowed intervals like thirds and sixths to be used more freely. That changed the harmonic vocabulary significantly, which (as Goodall notes) makes the music of composers like Dunstaple and Dufay sound significantly more "normal" when compared to modern Western music, in comparison to their predecessors.
However, Goodall is incorrect that this says anything about triads. These vertical structures involving thirds and sixths were not viewed as "triads" or even as single "chords" at the time. Their motion and resolution was still dictated primarily by horizontal melodic motion and rules of counterpoint in individual voices. (This is actually the origin of the "laws of attraction and repulsion" that Goodall claims came from triads. Composers were just obeying the previous rules of counterpoint, but when doing this with third-based sonorities, some patterns emerged that eventually gave us modern tonal harmony.) The "triads" were only incidental vertical entities, not viewed as specific "chords."
It wasn't until centuries later (early 17th century) that the first real theories of the triad were introduced, likely due to the standardization of certain types of vertical progressions that gradually emerged in the 16th century. It wasn't until the 18th century that a full theory and understanding of triads in the modern sense was created. And it wasn't until the 19th century that that theory became a predominant one in understanding how harmony worked in Western music.
So, I personally think that Goodall is a bit inaccurate in saying that "triads are the chords around which every harmonic, or chordal, journey is structured" since the 15th century. More accurately, the introduction of third-based (tertian) vertical sonorities as consonances began altering the structure of Western music around that time. The idea of these third-based structures becoming "chordal journeys" in progressions was an concept that very gradually emerged over the next four centuries.
I do think Goodall hits on another important element of this introduction of tertian sonorities historically: it allowed the building up of larger-scale vertical textures that were still consonant. Many types of music in various cultures around the world never developed larger vertical structures, instead tending to focus on single melodies against a drone or heterophonic textures. Layering in more than a couple independent parts against a drone when improvising can easily lead to increasing dissonance and confusion.
The third-based harmonic patterns emerging in the 15th century also gave rise to improvisational methods involving those patterns, which were relatively simple and could combine three or more parts to create a coherent sense of consonant harmony. Around the same time, strummed instruments like lutes and guitars began to pick up on those patterns and use these new "chords" for improvisation too (which influenced the development of theories of triadic harmony in the ensuing centuries).
Western European music thus began to build in the possibility of increasingly large ensembles playing music that had a complex vertical (harmonic) structure, a rather rare development among world musics. I think that's the shift Goodall is trying to get at, even if his oversimplification actually confuses what was going on and the timeline a bit.
It's generally accepted that minimum three notes constitute a chord (not getting dragged into power chords here!). So basic harony in most pieces can be translated into chords that are built from three notes. In Western harmony, those notes are usually built with two thirds, often making 1,3 and 5 (2,4 and 6, etc) from diatonic notes.
It was found that three notes worked well together, so why not use them! Of course, extra notes could be added, as extensions, but the basic building blocks were those triads.
This is only an uneducated guess, but it might mean that musicians think of harmony in terms of triads. If you look at song books and "fake books" (there are fake books for classical tunes too), you can see that practically any piece can be reduced to a melody and accompanying chords (which are written as chord symbols). The essential basic backbone of the chords is either a major, minor, diminished or augmented triad. In addition to the basic triad there can be extra notes like sevenths adding more flavor and strength. The essence of pretty much any harmonic journey can be described as a sequence of triads.
You can play classical tunes on an accordion or an "arranger keyboard". Chord triads with the left hand and melody with the right hand. Like this, Mozart's 40th:
On top of the melody you can see chord symbols:
- Gm : G minor triad
- Cm : C minor triad
- D7 : D major triad with an added seventh
- Cdim : C diminished triad
- and so on
The lead sheet / fake reduction from the above video can be found on page 16 of the Yamaha PSR-110 arranger keyboard's manual: https://usa.yamaha.com/files/download/other_assets/0/318210/PSR110E.PDF
Acoustically the overtone series reinforces the tones of a major triad. A root position major triad (in open position) is a thing, a phenomena, from a scientific perspective.
Historically the triad was viewed as the harmonic foundation, sometimes called the perfect chord or the chord of nature.
In must theory a root position major triad is considered very stable and a harmonic goal or resting point. The movement of unstable harmonies to stable harmonies is a dynamic force in music.