#1
I was just wondering when would you use a half diminshed chord versus a full diminshed. I understand why they are named that (A half diminished is 1, b3, b5, b7 and a fully Dim is 1, b3, b5, bb7).

But I am wondering, if I was in the key of C major, what function would each type of
diminished chord have or are they interchangable.

Thanks for any help.
#2
and also...why not just play B diminshed chord in C major (B, D, F) as opposed to using these 7th type chords...what function does adding the minor or diminshed 7th have?
#3
In diatonic scales, (i.e. the major scale and its modes) the half diminished chord is the chord that is naturally built from the 7th tone. In the case of C major, the chord built from B is a half diminished chord.

Thus, it is used if your chord progression uses the vii chord, or often as a substitute for the V chord. It is also nice as a passing chord in many situations, since its voicing with the root on the 5th string (A) is very similar to that of a maj7 with root on the 5th string.

The full diminished chord, however, is not built from the diatonic scale, and is thus very dissonant. Most commonly, it is a passing chord to be used as a transition. If you want lots of dissonance, this is a go-to chord. Another interesting use is that since its note structure is not like most, you can play it with the root not in key, but have it sound alright since the other notes often will be. For example, if you a playing the Major scale, you can play a fully diminished as a flat sixth in the progression, and only the root won't be in the key.

Adding the 7th to the diminished chord does what it does for all chords: extends it and gives it more flavor. This is especially important for the diminished chords, as without the 7th it is ambiguous as to whether it is half or full diminished. Also, they can sound a little muddy without the 7th, so I would recommend it.
Last edited by In Vein at Mar 21, 2012,
#4
they are very different. a fully diminished chord generally has a dominant function, and is usually used anywhere you'd use a V chord a major third lower (in fact, some theorists go as far as to say that fully diminished seventh chords do not really exist, but are just a Vb9 chord spelled without the root). A half diminished seventh chord can technically have a dominant function (but it sounds considerably less dominant then a dominant chord or a fully diminished chord), because it contains a tritone which can be resolved to the tonic chord (A B half diminished seventh chord contains the B and F just the same as a G7 chord, which resolves nicely to a C major), but in contemporary music it is much more common to see it having a pre dominant function, as a ii in a ii-V relationship.
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#5
Quote by tehREALcaptain
in fact, some theorists go as far as to say that fully diminished seventh chords do not really exist, but are just a Vb9 chord spelled without the root


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#6
I'd just like to add that a fully diminished chord sounds good as a dominant in a minor key much in the same way you use the half diminished in a major key, i.e. viiº7 - i, just like viiø - I.

And as a rule of thumb, each of them might sound better than the other if its seventh is diatonic to the key.
#7
Use the half-dim chord pretty much anywhere as a leading-tone chord. You can approach almost any chord in any progression by a half step. Since it's the leading tone that really matters in the end, you can really play almost any chord voice from the leading tone's note.

One of the most common uses for the half-dim chord (m7b5 chord) is using it as a substitute for a 7th or 9th chord. You'd play a half-dim (m7b5) chord from the M3 of the 7th or 9th chord. IOW, for C7/C9 play Em7b5.

Why does this work so nicely? Because it functions as a rootless 9th chord. C9 has C E G Bb D, Em7b5 has E G Bb D...it's the same chord without the C note...so it's a rootless C9 chord...

and this is a bit of an example of the leading tone thing...in Blues in C, you can play the C7/C9 then just before you would change to F7, you'd play the Em7b5 chord...the E is the leading tone to F7. Make sense?

To take the leading tone a step further...make that "E" chord any type of chord, just resolve it to F7 and you should be good in most case. Yes, some chord names will sound better than others but once you hit the F7 chord all will be forgiven, so to speak...so experiment!
Last edited by MikeDodge at Mar 22, 2012,
#9
thanks for the replies everyone...but something has come up which I am also confused about.

In Major, a half diminshed chord is diatonic right? Wouldnt the half diminshed chord be diatonic as well in the relative minor?

For example, in C major, B half diminshed and in A minor, B half diminshed?

But then, if the B half diminshed operates more as a predominant...why is often substitued with the dominant V chord in both Major and minor.

Sorry, I am just confused. Any help would be appreciated.
#10
but it is diatonic in the minor too, it occurs in the second degree
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#11
Quote by dvm25
thanks for the replies everyone...but something has come up which I am also confused about.

In Major, a half diminshed chord is diatonic right? Wouldnt the half diminshed chord be diatonic as well in the relative minor?

For example, in C major, B half diminshed and in A minor, B half diminshed?

But then, if the B half diminshed operates more as a predominant...why is often substitued with the dominant V chord in both Major and minor.

Sorry, I am just confused. Any help would be appreciated.


A B half diminished in C Major has a strong pull to C, as it is the leading tone. It acts as a dominant, however using a V7 has a stronger pull to I.

In minor, however, your "tonic" chord is Am. So in this case B half diminished, it acts as a ii chord (normally pre dominant) however, diatonically speaking it happens to be a diminished triad. Still has a predominant function.

You do understand that
Major:
I ii iii IV V vi viidim I
Minor:
.................i iidim III iv v(or V) VI VII (or vii full diminished)
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#12
I swear I'm going to quit playing guitar because of this thread... okay maybe not. But I definitely feel like a noob =( Music theory hard. I ALMOST grasp what you guys are trying to say because I know a bit of theory, but it makes my brain hurt. I still don't know enough about chord progressions and strange chords. I AT LEAST know how to use whatever key you're in to get the scale, to then get your chords based on the intervals, but it's like doing trigonometry every time for me. I literally can't just see a crazy chord name and know how it will sound or what made it up.

I'd love for you guys to post some good reading materials for me to brush up on these topics. I would LOVE it if someone could post a thread/column/article on how to APPLY these to the guitar to LEARN it, rather than just reading it and trying to comprehend.
#13
Quote by dvm25
thanks for the replies everyone...but something has come up which I am also confused about.

In Major, a half diminshed chord is diatonic right? Wouldnt the half diminshed chord be diatonic as well in the relative minor?

For example, in C major, B half diminshed and in A minor, B half diminshed?

But then, if the B half diminshed operates more as a predominant...why is often substitued with the dominant V chord in both Major and minor.

Sorry, I am just confused. Any help would be appreciated.

It's usually not. You don't often see people resolving the Bdim to C in C major...Not to say you can't...

In a classical setting sometimes m7b5 functions as a dominant. In a minor key, on the ii, it will never - it's a predominant.

In jazz, m7b5 is never dominant EVER. Even in classical it's rare to see a m7b5 resolve that way - they usually just make it a dim7 - even if its not diatonic. You're more likely to see Bdim7 to Cmajor than Bm7b5 to C major...
Last edited by chronowarp at Mar 22, 2012,