10

I'm working through "Guide to the Practical Study of Harmony" by Tchaikovsky and I had a question about this section on triads (he's working with a C Major scale):

The whole mass of major and minor triads may be grouped into three sets of two triads each: One, the tonic group viz: the triads on the 1st and the 6th degrees. Two, the dominant group viz: the triads on the 5th and the 3rd degrees. Three, the subdominant group viz: the triads on the 4th and 2nd degrees.

Now, I get why the 1st and 6th triad are in the tonic group. I also get why the 5th triad is in the dominant group and why the 4th triad is in the subdominant group. But, I'm having a hard time understanding why the 3rd triad is dominant and the 2nd triad is subdominant.

I'm not sure how I'd categorize them, and I suppose they have to placed somewhere, but I'm not sure why they're being placed here.

I Googled around some and found some conflicting information on Open Music Theory which has muddied the water further:

If you are already comfortable with Roman numerals, you can generally think of I, III, and VI as tonic, II and IV as subdominant, and V and VII as dominant. (Though, as you will see below, there is more to it than that.)

I suppose I'm just looking for some clarity here. It's important that I understand why Tchaikovsky is placing the 3rd and 2nd triad where he is as I keep plowing through the book. Thanks for the help!

krebshack
  • 153
  • 1
  • 9
  • The only thing I can think of is that, if you're creating a group of minor triads, that, in that case, the 3rd triad would take the same place that the 5th triad does in a grouping of major triads. I'm not sure that this is right, though, and I don't know how to reconcile that with the Open Music Theory entry. – krebshack Jun 03 '18 at 22:51
  • Not an answer, just a comment, but in a sense, vi is the relative minor of I; ii is the relative minor of IV; and iii is the relative minor of V. – Jim L. Dec 17 '19 at 20:59

2 Answers2

14

The chord built on the sixth degree of the major scale is closely related to the I chord, and similarly the chord built on the second degree is closely related to the IV chord, and the chord built on the third degree is closely related to the V chord. The I, IV, and V chords have tonic, subdominant, and dominant functions, respectively, and the vi, ii, and iii chords (sometimes called parallel chords) are sometimes called tonic-parallel, subdominant-parallel, and dominant-parallel, respectively.

In the key of C Major, the I chord contains C-E-G, and the vi chord contains C-E-A; that is, the vi chord can be formed by raising the 5th a whole step. Since the vi chord shares the root and the third of the I chord, it can function as a tonic chord. The fifth of the I chord is relatively unimportant, so you might think of the vi chord as a I6 chord. There are no other triads in the key that share the root and third of the tonic chord.

The same considerations can be applied to the ii and iii chords. In the key of C Major, the ii chord contains D-F-A, and the IV chord contains F-A-C; these share the root and third of the IV chord, so the ii chord can function as a subdominant chord. The iii chord contains E-G-B, and the dominant V chord contains G-B-D; these share the root and third of the V chord, so the iii chord can function as a dominant chord.

  • 1
    I thought the parallel chord of C maj was Cm, parallel of F maj was Fm, and parallel of G maj. was Gm. Relative might be a more appropriate term, as the relative of C is Am., relative of F is Dm., and relative of G is Em. – Tim Jun 04 '18 at 05:57
  • 1
    @Tim -- in this usage parallel chord and relative chord have the same meaning; the terms come from Riemannian theory. There is a link in my answer to a Wikipedia page about this. But I think the bottom line is that the I chord and the iii chord are the only two chords that share the root and 3rd of the tonic. –  Jun 04 '18 at 06:17
  • I=CEG, iii=EGB. Sharing three and five of the tonic? The only one sharing the root of the tonic is IV. I find it strange that the term parallel can be used here, regardless of who came up with a theory. It just sounds confusing - to me. When terms already exist, and have specific, different meanings, where's the mileage in making them both mean the same? – Tim Jun 04 '18 at 06:37
  • @Tim -- sorry, it's late and my brain is shutting down. I meant the I chord and the vi chord both share the root and third of the tonic chord, as I wrote in the answer above. –  Jun 04 '18 at 06:38
  • @Tim -- I don't see the terminology as confusing; it connects the I chord to the vi chord, the IV chord to the ii chord, and the V chord to the iii chord with a name that underscores their relatedness. There are loads of overlapping terms in music anyway; I think that these date from the late 1800's. The Wikipedia page suggests that the "relative" and "parallel" conflation has to do with translation from the original German. –  Jun 04 '18 at 06:47
  • Exactly. Relatedness sums it up. Relative. Parallels just don't ever meet, let alone have relations! It seems to be confused by translation, something I'll check on later. Just that in most other people's (apart from Riemann's) world, the two terms are absolute, and often used, with no confusion. He seems to have introduced some, or perhaps it's just his native language. Thanks. – Tim Jun 04 '18 at 06:55
  • My last comment! Yes, the German for 'relative key' is 'paralleltonart'. Confusion reigns! However, that spawns the questions - if the parallel chord of C is Am, what's the relative chord? If the relative key of C is Am, what's the parallel? Might this be confusing to a beginner, if it's confounded me..? – Tim Jun 04 '18 at 07:12
  • @Tim if beginners want to get confused with Riemannian theory, that's their problem (or their teacher's problem if they have one). The Tchaik theory book is historically significant as the first ever textbook on Western music theory published in Russia, but from contemporary accounts Tchaik regarded teaching theory as a boring duty, having accepted a friend's offer of the post of Prof of Music Theory at the newly opened Moscow Conservatory mainly for the salary and the prestige of the title "Professor" than for anything else. –  Jun 04 '18 at 11:45
  • @alephzero -- note that OP never mentioned Riemannian theory; I only used the names dominant-parallel, etc. because those names connect the iii chord to the V chord, etc., then mentioned Riemann in a comment when Tim wondered about the terminology. Since it wouldn't change the important part of the answer, maybe I should have left this part out if it causes confusion, though it didn't seem to for the OP. –  Jun 04 '18 at 12:25
  • @Tim -- I have edited to reduce references to the unsavory terms and hopefully increase clarity ;) –  Jun 04 '18 at 12:43
  • @DavidBowling - It probably would not cause confusion to the OP, as he's maybe never encountered terms such as that previously. ( One can't get confused with what one isn't cognisant of). OP to respond? – Tim Jun 04 '18 at 19:56
  • @alephzero - really don't think anyone 'wants' to get confused with anything. Sometimes it's thrust upon us! Being the 'first ever' doesn't give a lot of credence if it's not concrete enough... Who was the first to state the flatness of Earth..? – Tim Jun 04 '18 at 20:00
  • I am an absolute music theory noob, but what resonates with me in this answer is how well the parallel chords can work as substitution. Case in point is "Can't Help Falling In Love" by Elvis Presley which at least in one arrangement goes like I-iii-vi, IV-I-V. I've tried I-V-I IV-I-V instead, (as well as I-V-I ii-vi-V) and they all work perfectly well. – David Airapetyan Dec 19 '21 at 20:58
0

Why is the third triad dominant?

It is not. The third triad is the mediant. The triad on the fifth degree is the dominant.

The selected answer is misleading about the substitute nature of the mediant triad. Apparently the answer take a Riemannian view without pointing out the ambiguous nature of the chord. The mediant chord shares two tones with the dominant chord, but it also shares two tones with the tonic. There is no clear way to simply say the mediant chord substitutes one or the other chords.

This definition from the Harvard Dictionary of Music summarizes the point well...

enter image description here

It should be understood that such substitutions lead toward ambiguous tonality. That is not a problem per se, but cadences won't have their proper function if chords are substituted. V iii, iii I, etc. won't work as perfect cadences.

Michael Curtis
  • 56,724
  • 2
  • 49
  • 154
  • I did not take a Riemannian point of view, and we did discuss this in the comment thread under my answer. I specifically took the point of view that the iii chord can (not must) function as a dominant because it contains the root and third of the V chord. I only mentioned dominant-parallel as an existing term (which happens to come from Riemannian Theory) that describes this relationship, providing a link for anyone who would like to read more about that. –  Feb 21 '19 at 18:08
  • My point is to make clear the ambiguity. – Michael Curtis Feb 21 '19 at 18:15
  • I agree that there is some ambiguity, as there is likely to be with substitutions, but the iii chord contains the root and third of the V chord, yet contains only the third and fifth of the I chord. This would seem to make it less likely that the iii would find itself in the role of the tonic. –  Feb 21 '19 at 18:25
  • ...and if we return to the Harvard Dictionary article we see that kind of isolated determination is a problem. The substitute character of either tonic or dominant isn't about those chord tone comparisons, but about the mediant chord's use in the surrounding harmonic context. Basically, it's problematic to simply say iii subs for V – Michael Curtis Feb 21 '19 at 19:33
  • Probably the best example I can think of now is a deceptive progression like V4/2 iii, if the iii was indeed simply a sub for V that kind of deceptive progression wouldn't be sensible. In that harmonic context iii clearly isn't acting as a dominant. – Michael Curtis Feb 21 '19 at 19:39
  • Of course, context is always important, however, I never said that iii simply is a sub for V, or that iii will always function as a dominant. The article you cite says: "The chief substitute for each of the three principal triads is its relative minor; thus... III for V...." This is what was suggested in my last comment ("less likely that the iii would find itself in the role of the tonic.") As I said, I agree that there is some ambiguity, and good of you to point this out. –  Feb 21 '19 at 19:47
  • After the introductory stuff you concluded "so the iii chord can function as a dominant chord" with no mention of possible tonic substitution and the ambiguity, nor mention of the importance of context. The problem is using such an answer as the basic to close duplicate questions. – Michael Curtis Feb 21 '19 at 20:19
  • Yes, I said can, not must or always. That is correct, and the duplicate question was "are there cases where the mediant chord has a dominant function." The answer is yes, and I don't see any way in which this question is not a duplicate of that one. Also, it is not the answer which is the basis of the closure, but the question. Others are free to post additional answers here, as you have. –  Feb 21 '19 at 20:25