# Why is C the tenor of phrygian?

After teaching some students about medieval church modes, I took a question as to precisely why the tenor/confinalis of phrygian/mode III was C rather than B. I answered according to what I had been taught: that tuning of B was unstable (generally sharper) and the note could not function as tenor.

It wasn't until later that I started asking myself why tuning was problematic for B. My understanding is that Pythagorean tuning was the most widely adopted approach during the middle ages, and there's no obvious reason why Pythagorean tuning would produce clashes relating to the note B that don't occur on other pitches, and in other modes. e.g. Even though B is at the end of the cycle of fifths, and has the most 'distance' to other notes in the diatonic set, if the tuning is Pythagorean then the whole tones are still 9/8 and the semitones are 256/243. So, unlike other just scales, the tones and semitones are not of different sizes. Other somewhat awkward intervals that arise (e.g. the ditone between B and G) occur in other modes (e.g. in Dorian, between its tenor A and F)

Also, if the tenor was B it would still be a 3/2 perfect fifth above the final. Even if the tuning was based on something like Ptolemy's tense diatonic, that would also preserve a 3/2 perfect fifth between E and B.

The only non-tuning related answer I could think of was that it may be problematic to place the emphasis on one of the notes of the diatonic tritone, but other modes (e.g. hypodorian) do just this.

I scoured grove, google, and every physical source at hand. Two sources cited non-specific 'tuning issues' as the reason. Two sources explained it in terms of the fact that C was the reciting tone in the related psalm tone, but that just defers the question (e.g. why is C the reciting tone in mode III, rather than B?).

So, I'm still left wondering what was in fact 'unstable' about the tuning of B, and why it was avoided as tenor/confinalis. Any advice appreciated.

• I am not an expert, but it might have something to do with the tritone between the very prominent phrygian 2 and the 5, or it might be that the B is a bit strange in phrygian, as is only comes from the tetrachordum durum, while the F can only come from the naturalis or the mollum. But anyway, just think about how strange that question must sound to people who do not know this terminology: Why would C be a tenor, and what is phrygian?
– Lazy
Jul 25, 2023 at 19:13
• Thanks! I had considered that stressing one of the notes of the diatonic tritone might be relevant, however Hypodorian treats F as tenor too? Another consideration I considered was whether the other note of the tritone is used in the psalm tone figures, but the 3rd psalm tone doesn't use an F in its Introitus or Mediant, so I still can't work out why one would preference the C over the B. The durum v molle connection might be a more relevant lead indeed - I hadn't considered that, so thanks again! Jul 26, 2023 at 13:29
• Much belated but found this in Jeppeson's Counterpoint, suggesting you may have been on the right track: "Originally B was actually a dominant; later - presumably about the year 1000 - the dominant function was transferred to C, apparently because by that time musicians had become more sensitive to the dominant relation B-F and consequently did not wish to accept, for such an important place as the dominant, a tone that might so easily produce a dissonance." Aug 29, 2023 at 13:26