# What's the exact difference between modulation, key change and tonicisation?

I've always regarded a key change as the use of a completely different set of notes for the following music - definitely in a different key. Was in C, now is in C#, with no reason to suppose a return.

Whereas a modulation is a more subtle move, perhaps to the parallel, or relative key (C>Cm, or C>Am) or the the IV or V (C>F, or C>G), where there's a lot of common ground between old and new, and indeed, there's a very good chance there'll be a return to the 'original key' at some point.

The terms seem to be used interchangeably, so what's the truth of the matter?

I think your intuition is mostly correct when it comes to modulation. I would make only one small adjustment: most scholarship tends to view a change in tonic as different from a change in mode. In other words, moving from C to G is a modulation because we change the tonic pitch, but moving from C major to C minor is "just" a change in mode. Thus we see that "using new pitches" isn't enough to effect a modulation, it's actually changing tonic. (By this logic, one could say that changing from C Ionian to E Phrygian is a modulation, even though there are no new pitches.) As you've suggested, modulations—especially in music of the common-practice period—tend to return to their home key.

A key change can be one of two things. It can either be a physical spot in the score—the key signature changes here from C major to E minor—or a moment when the music leaves one key and moves to another one (either with or without an explicit key signature change). I think it's often a bit like the square vs. rectangle issue: not all explicit key changes in the score are modulations, but I'd say that all modulations are key changes.

You'll notice that "key change" in this latter sense (moving to another key) is thus synonymous with "modulation." I don't personally see any clear distinction between the two in terms of relationship to the prior key and whether or not that prior key will return.

Tonicization is often taught as a brief foray into another key. There's usually some gray area here in terms of how long a tonicization must be before it becomes a modulation, and it's only made worse when we discuss notions of "extended tonicizations." But I think there's a very good rule here: if there's no cadence in the subsidiary key, it is not a modulation, but a tonicization. Once we use this cadential rule as a limiter, it becomes much more clear when something merely tonicizes and when it actually modulates.

Lastly, all of these are further confused when you read past theory treatises. Many authors of yore use "modulation" the way we currently use "tonicization," which certainly doesn't help at all.

(Thought-provoking question, as always!)

• Thanks, hence the question. Can't help thinking there's more than a tenuous link between 'modulation' and 'mode'. But the terms do get bandied about as synonymous, and I, as you do, don't think they are. – Tim Sep 4 '18 at 16:42

Richard's answer is correct. Current (2018) usage is that "modulation" and "key change" are identical. "Tonicization" generally means a really short chromatic sequence involving a secondary dominant; for example in C-major, one may have a quick A7-d chord sequence; the d-minor chord is tonicized for a very short time.

Looking at some of the earlier harmony texts (1800s to early 1900s), the term modulation was also used for these short sequences. Some texts seem to indicate a short melody as changing keys with every chord change. The E7-A7-D7-G7-C pattern is rather common (in ragtime among other genres) but it doesn't seem to change from C-major. The earlier usage would have analyzed it as a sequence of keys: A-D-G-C with the "tonic" elided. Later usage (tonicization) is a bit better but in this case, I would analyze the E7-A7-D7-G7-I as a single pattern III7-VI7-II7-V7-I rather than as (V7/VI)-(V7/II)-(V7/V)-(V7)-I. A "modulation" or "key change" (in my opinion a key change should be "longer" or weightier with perhaps a ii-V-I or the like in the new key.)

A bit of terminology: "modulation" in radio (and other fields) means adding small changes to a main signal. I think I read somewhere that in the fifteenth or sixteenth century, modulation was used in this manner. The idea was to reinforce the key (or mode?) of a phrase or line by making a few digressions but returning; it's a bit like the radio usage. This describes "tonicization" too but modulation would refer to the main line whereas tonicization emphasizes the out-of-key chord. We probably can't go back to the earlier terminology as then we would have no word for "key change."

One more thing, Schoenberg (and others using other terminology) suggests that a true key change involves neutralization of the characteristic notes of the first key. Going from C to F would mean emphasizing the Bb as that is different note.

• Indeed, your last para. In sheet music, it's denoted (literally!) by use of natural signs followed by the new key sig. – Tim Sep 5 '18 at 6:21
• @Tim, not necessarily. Going from C to F naturalizes nothing in a key signature, but only adds the Bb. Or, going from D to A only adds a sharp. The neutralization of the previous key is not always noted in the score. – Heather S. Sep 7 '18 at 11:26
• @HeatherS. - you're correct, but I couldn't find a simple way to couch what I meant. One needs to read between the lines, but then one ends up with FACE..! I think the naturals are mostly put into a key sig. when it goes from, say, E to A, or Eb to Bb, although I remember loads of music where everything was cancelled with naturals, then the new key sig. written. – Tim Sep 7 '18 at 13:18
• I haven't seen a situation where sharps were canceled in order to go to a signature where more sharps were added, but, yes, anytime the piece moves to fewer flats or sharps, or changing from one to another (say from F to D) naturals are usually placed in the key signature as a courtesy. It is interesting in modern pieces the use of flats and sharps in front of notes or in key signatures has no rules. Some are mixed sharps and flats, some do not follow the "barline rule", some have every single note marked sharp, flat, natural. (My teacher suggested I do the latter in one of my pieces.) – Heather S. Sep 7 '18 at 14:59
• Neutralization isn't a key signature thing; it's using the form of the note in the new key as opposed to the form in the old one. Going from C to G means using a F# rather than an F (and making it sound that this is the "preferred" version) to show a modulation. Playing a D7-G cadence then following by C-F-C-dm-G or the like indicates a tonicization instead. – ttw Sep 7 '18 at 16:24