# Why has the vi chord no tonic function, i.e. what gives a chord its function?

I can totally say that the vi chord could not work as a tonic, feeling deceptive and so on and I'm wondering why. Could it be that a chord sounds "tonic" only if it is the tonic, namely C-E-G. So also any inversion of the tonic chord won't have a tonic function. Or we can maybe better say that there are several shades of tonicity (or of finality), where we could give the

I->100%,

Ib -> 70%,

Ic -> 40%

and vib 20%, since it is still super-dominant (say, 70%) and a still sub-dominant (10%). Clearly here numbers are not the result of a deep inquire, I'm just trying to use a rough example to explain a possibly silly concept =D

As for the second part of my question, for example, the iib chord acts as a sub-dominant and the vii°b chord as a dominant, but then why can't a iiib chord act as a dominant and why is it not (usually, as far as I know, which is not so much) used in that fashion?

[Here by b and c I mean the first and the second inversion of the chord]

• You probably mean b and c are first and second inversions, respectively. – Tim Nov 20 '16 at 5:20
• Just for future reference the B and C in the question are referring to inversions. – Neil Meyer Nov 20 '16 at 17:51
• Uh, sure, b is the first and c is the second. I'm used to think of a as the first, sorry. I'm editing it now. – Alex Doe Nov 20 '16 at 21:01
• A cadence like V-vi (often called "deceptive") can be interpreted as the vi exhibiting "tonic function". – Brian Tung May 10 '17 at 21:37
• `I iii vi` `i III+ VI` tonic function, `ii IV` `iio iv` subdominant function, `V viio` `V viio` dominant function. – user53472 Jan 17 '19 at 13:41

Different theoretical traditions use different terminology, so it's possible my answer contradicts whatever tradition you learned from (for example, I've never seen your a, b, c notation for inversion. I'll use 6 for first inversion and 6/4 for second).

At any rate, the textbooks I learned from and taught from (I've studied and taught exclusively in America fwiw) say that vi indeed can have tonic function. To the extent that tonic function is defined as a resolution of dominant function, vi in root position is considered to have tonic function. Obviously, it can't be ultimate tonic function, but it can substitute for the I chord in these contexts; some textbooks prefer to refer to it as tonic substitute function for that reason. By the way, your example of V-vi6 is generally not done in this style. It tends to sound like V–I with a wrong note. In fact some theorists don't even call the chord vi6 when it does seem to happen, preferring to hear it as a I with embellishment.

I agree to some extent with your hierarchy of finality, V–I6 is indeed weaker than V–I. However, I6/4 doesn't really have tonic function at all in the vast majority of circumstances. More often than not, what looks on the page like a I6/4 is actually just an embellishment of V—usually called a cadential 6/4 chord. Its function is dominant, or, rather, an embellished dominant function.

Does this make sense?

EDIT TO ADD: Oops, forgot your other question. You're right that, because the leading tone is present (in major keys), the iii chord seems like it could have dominant function. However, in reality, this is virtually never the case. If you look at the notes of a iii chord (in C major, E-G-B) it shares just as many notes with I as it does with V. This makes it not particularly useful for either function, and this is why iii is actually quite rare in common-practice tonal music, with the exception of sequences or as a push toward the relative major in minor-key pieces. When in does occur in major keys outside of sequences, it tends to more often be used as a substitute for I6 or other embellishing roles. That being said, there are exceptional cases where you might find a iii used for dominant function, they're just very rare.

• If a chord is to act as a dominant, it needs a note that acts as a leading-note. If the B of iii resolves onto C, the options for the following chord are iii-I (two notes already in common, and iii sounds like an embellishment of I) iii-IV (parallel motion, without careful voice leading, and IV doesn't have any tonic function) or iii-vi, (a perfectly good "modal perfect cadence," but not the original major key "tonic"). – user19146 Nov 19 '16 at 20:12
• The a.b and c notation for inversions do exist. Our local institution that provides theory exams even aknowledge it as valid. It is just generally frowned upon as it teaches very little in the way of comprehension. – Neil Meyer Nov 20 '16 at 17:50
• @NeilMeyer Interesting. Out of curiosity, where is that? Doesn't seem inherently bad to me exactly, just unfamiliar. – Pat Muchmore Nov 20 '16 at 18:13
• UNISA (University of South Africa) – Neil Meyer Nov 20 '16 at 18:15
• iii is not rare. It has tonic function. Try playing either `I - iii - IV` or `i - III+ - iv` on a piano. – user53472 Jan 17 '19 at 13:38

Besides the inversions (the bass note changes), you also have the "position" (the soprano note plays a root, third, or fifth).

The proof that the sixth degree can be tonic is the deceptive cadence. Besides, it IS a tonic in the "relative" minor.

"Tonic" is a harmonic "function", and there are only three. A diatonic scale has 7 degrees, so, in certain contexts, certain chords can "steal" the harmonic function.

• I've edited your "'parallel' minor" to say "relative"; I assume you are discussing the relationship between C major and A minor, which in English are "relative" keys. Feel free to rollback the edit if you feel I've changed your intent. – Richard May 9 '17 at 13:37
• @Richard You are right, I should know this, but my terminology is rusty. On the first edit, I would like to point out that by "base" I meant the primary note of the chord, which, in my humble opinion, is not always the "bass" note of the chord. Do leave the edits, they are logically sound. I have a good grasp of English, but expressing thoughts in a conicse manner is another thing. Cheers. – Hatebit May 9 '17 at 13:42
• Agnes, no worries at all! It's especially tricky because our "relative" is actually "parallel" in German (!). And I've edited your "base" to "root"; that was a silly error on my part, and I apologize. – Richard May 9 '17 at 13:47
• @Richard, it's all right, all edits are welcome, I take no offence, this is a public website. I do have a multi-lingual dictionary of music terms, about time I put it to good use... – Hatebit May 9 '17 at 13:49