Music Theory

It means that "The Third Tone facing / following Fa is the DEVIL in music"

Which KEY is it?

It is B2 (B MAJOR)

or the SEVENTH WHITE KEY (just previous to C2.)

Freely translated, it means "B versus F is the very devil for us poor musicians!"

This is actually rather a complicated question, but it's interesting all the same. I'll try to keep it as simple as I can.

"Mi" and "fa" represent notes of the mediaeval musical scale. Their system of scales was not like ours. Nowadays we use a basic scale of seven notes ("degrees"):

do re mi fa sol la ti/si (traditional spelling).

In the Middle Ages, the theoretical basis was a scale of six degrees; it was called "the hexachord" (= "the six notes"), and went like this:

ut re mi fa sol la

C D E F G A

(These notes constituted the "natural" hexachord).

No B. B was regarded as having two alternative tunings, which today (in English) we call "B-natural" and "B-flat" (written "Bb" below). These two B's were accounted for by transposing the hexachord to begin either on F:

ut re mi fa sol la

F G A Bb C D

(called the "soft" hexachord, because "soft" was the usual word for "flat"),

or on G:

ut re mi fa sol la

G A B C D E

(Called the "hard" hexachord).

The hexachords were originally a way of dealing with melody. Choral music would involve different voices singing different melodic parts all together, so different hexachords would occur simultaneously. So if the harmony was to "work" correctly performers really needed to know which version of B was to be used at any one time. Composers seldom bothered to say, and performers took pride in not having to be told. (Which only goes to show...)

To take account of either soft or hard B, a singer had to mentally switch from one hexachord to another (equivalent to what a modern singer does when reading music which changes key). If you look at the three hexachords, you will see that the notes E and B are called "mi", and F and B-flat are called "fa". (F as "ut" and E as "la" cause no problems). The notes "mi" and "fa" (B-F, E-Bb, B-Bb) will occur together in harmony when different "voices" are using different hexachords.

Here is the problem:

In mediaeval musical theory, harmony was based on the contrast between

1. concord ("agreeable" combinations of notes - simple "chords"), and

2. discord ("disagreeable" combinations - complex "chords", clashes).

　

The most important concord was the "perfect fifth", as between the notes C and G (covering a total of five degrees C-D-E-F-G).

All the notes of our natural scale can be arranged into pairs which each constitute a "perfect 5th":

C-G, D-A, E-B, F-C, G-D, A-E;

EXCEPT B (mi) and F (fa).

Sounded together, B and F produce a discordant-sounding "diminished" 5th. In a single voice-part, a B next to an F might prove difficult to "pitch" correctly, given what people considered to be "musical" at the time. This is why B doesn't form part of the original "natural" hexachord. B and F together were considered very ugly. B and Bb together were really really bad.

To correct this discord in harmony, or to make a less ugly and more "natural" melodic line, either B has to be tuned down (B-"flat"), or F has to be tuned up (F-"sharp": creating an "unofficial" hexachord).

The same discord arises between E (mi) and B-flat (fa) when you change from the first hexachord to the second in melody or combine the two in harmony.

And B (mi) with Bb (fa) was completely beyond the pale, because notes with the same name need to be tuned the same to avoid "out-of-tune" clashes.

So, in early singing methods and in early harmony "mi contra fa" summarised a number of practical problems in interpreting written music, especially as musicians were expected to use their own discretion in deciding which tuning of B to use.

Hence the phrase.