I was fortunate enough to have a University lecturer (by the name of John O'Donnell) who was well up in the ins and outs of musica ficta. He managed to establish to at least my complete satisfaction that the circumstances under which most Renaissance vocal polyphony was performed (no score, no pencils, whole choir gathered around a partbook) meant that a heck of a lot of simultaneous false relations were unavoidable and must have been part of the sound. The reason they're now more closely associated with the English repertoire is that the English composers actually notated what continental composers in general left up to the ficta conventions...

Technically 'false relation' usually describes the use of the same scale degree in two different inflections in adjacent chords (which in common-practice harmony is one of those 'errors' like parallel fifths); the crunchy effect we're talking about is sometimes called a simultaneous false relation as I called it above. C# against D wouldn't technically be a false relation; Db against D would be, although not being particularly clever I can't see why Mahler wrote the note Mabel's talking about as a C#!

There are some lovely ones in the slow movement of the Brahms clarinet quintet, the downbeat of bar 8 for example...

Just very much enjoyed that Largo, Chafing Dish, thank you for the link. It is indeed a delicious moment at 3'37". For me, a clash in harmony like that is highly effective because the resolution is such an immediate relief - the false relation creates a fleeting but very intense moment of suspense.
I don't know this CPE Bach concerto at all. I will be looking/listening out for it now. 


This is interesting, Oliver.
I love this quintet but I don't remember false relations in the slow movement. Haven't heard it for ages, must borrow the score and listen to it.

Oo! Please sir! Please sir! Me sir! Me sir!

Here's one of my favourites. Mozart piano concerto no. 9 KV 271, slow movement. Have a look at the downbeat of bar 9.



Now this being 1777, that trill starts on the upper note, probably dwelt on a little with something of a light stress. (We all know the feeling.) That means that on the downbeat itself are sounding F natural in the 1st violins, F# in the violas, and G in the oboes.

Fair fell out of my chair when I first heard that.

...and here's the Brahms while I've got the scanner warmed up. Downbeat of bar 8, as I said (I think) - A# in 1st violin, A natural in 2nd violin.

I always find this false relation very striking, from the last movement of Ein deutsches Requiem (bar 52):



In no sense a smooth harmonic transition, more of a sudden discontinuous shift, almost like a change of gear, perhaps to denote a certain exaltation at the thought of God's work?

Wonderful Oliver! (Both you and the false relation!) Mozart really relished that one - with the forte marking too. Nothing subtle about it!

Many many thanks for going to the trouble of sending it. (My comment wasn't intended as a hint that you should!) This board's a constant source of entertainment and education for me.