# Which roman numeral should I use for F# diminished chord in the key F Major?

In the key of F major, what roman numeral is the F# A C chord? I know it is a diminished chord. It is going from a F to F#dim to Gm7

• I would write bii°. Nov 30, 2014 at 18:44

Using Roman numeral analysis you can look at it as a I - viio/ii - ii7 in the key of F, but I would look at it slightly differently see below.

Roman numeral analysis doesn't work in all cases and in fact I wouldn't give this chord a roman numeral since it is a chromatic passing chord between two chords in the key.

Think of it this way you are going from I to ii7. The F#dim is sandwiched in between the two chords and the F# can be perceived as a chromatic passing tone between the F and G. Because in the F# diminished the A and the C are common, the F#dim can be seen as an altered version of the I chord and thus the harmony from the analysis standpoint doesn't change.

If you really wanted to use a Roman numeral you could use a secondary dominant to describe the progression as a viio/ii making the whole progression I - viio/ii - ii7. I personally think just saying it is a passing chord is what makes most sense, but this is also a valid way to look at the progression.

• I like your thought process. In most cases this would make sense to me but if the chord were to last for a relatively long duration, I would tend to think of it as needing its own designation. I also can't help but be reminded of being in school studying this; I imagine my professors would most likely have wanted me to call it a vii/ii unless it were for a very brief time, in which case it would just be a chromatic passing tone. So from an analytical standpoint, I would say it depends on whether you are looking at it on a micro or macro scale. Dec 1, 2014 at 14:30
• @Basstickler I agree it would depend, however I just wanted to point out that there are scenarios where the chord would not need direct analysis. I've seen many people try to incorporate every non-harmonic tone into an analysis and not realize it is counter productive to describing the harmony. Your right it's how you look at it. When I saw it I immediately thought passing chord, but listening might have yield a secondary dominant as the analysis I suggested states.
– Dom
Dec 1, 2014 at 14:41
• Reading back on your answer and what I wrote, I think most of it was more of a reiteration with different words. The main distinction or thought process I was attempting to bring to light is the academic side of things and, though I didn't explicitly state it, if you're going to hand in a roman numeral analysis assignment, you should probably mark that note and explain why it does not have its own roman numeral. In short, I agree with your answer and you get +1 and my comment is more for the OP in case this is for a school assignment. Dec 1, 2014 at 18:38
• @Basstickler, even heavily accented and of non-negligible duration, the F♯ is probably going to come off as a non-harmonic tone. However, if your prof was teaching common practice harmony, I suspect you would not have seen this example: especially with the 7th in the last chord, unless there are first inversions involved somewhere, avoiding parallels in this example is not going to be a doddle. I won't say that it can't be done, but it would involve a lot of movement by skips in the upper voices, which may not be very convincing.
– user16935
Jan 2, 2017 at 17:45
• Question: When the target chord is G, isn't the chromatic chord an G#? (You go one half step up from the root of the target chord). (My source of knowledge) Apr 26, 2020 at 19:07

It could be written as vo or iiio as both of those notes feature in the diminished chord. Could even be bviio as an Eb may also be played. However, as the lowest note is apparently an F#, it could also be written #Io,(#io) although I've never seen that written. The lower case seems to be used to indicate a 'minor' chord, as a diminished has a minor third.Couldn't find much about this while searching.

It MAY not be a diminished chord, though. It could be the dominant of that Gm, without the root. (D) F# A C. This would put the Roman numeral as VI7.Or, as Basstickler points out, V7/ii7.

• I'm not sure I can agree with your analysis, though I do see where it comes from. The way the question is stated, it sounds like this chord would only have F#, A and C, so I don't think it would make sense to call this a vo, iiio, bviio or VI7 w/out the root. In any of those cases, not all of the notes that spell out the suggested analyses are there. For all but the VI7 (which I would call V7/ii) this would definitely make more sense if it were a fully diminished 7 chord. I also can't say that I've heard of a #io, as this would most certainly have a secondary function. Dec 1, 2014 at 18:57
• It could (and in this case does) act as D7 minus the root, just as the full diminished 7th chord can act as D7b9 minus the root. But that doesn't mean it IS that chord. If Roman number analysis can't cope with the very common F, F#o, Gm sequence, get a better system! Jan 2, 2017 at 13:54
• @LaurencePayne - it probably is a secondary dominant to Gm. So it would, in that case, be V7/ii7. As far as I know, it's the best system we have, some of NNS works well, but some leaves me wanting! What else is there?
– Tim
Jan 2, 2017 at 14:05
• "What else" is a notation that allows a diminished triad on the shartened tonic, a very common thing. We don't insist on calling IV "ii7 with the root omitted". That's a step down the rocky path that leads to Db7 being labelled "G7, with the root and 5th omitted". Even if that is what it sometimes acts like! Jan 2, 2017 at 16:37