Secondary dominant

V7 before any chord (regardless of the functional degree)

I didn't understand

Classic C progression:

C+ Dm- G7 Am-

can become:

C+ (A7) Dm- (D7) G7 Am-

---

A7 and the V7 of Dm-

D7 is the V7 of G7

But in plain words, what is the secondary dominant?

Go back to my first post, the dominant (V7) of the degree that follows it...

and what is it for?

Fox wrote:

and what is it used for?

To expand the tonal discourse, to emphasize certain degrees by turning them into tensions, to modulate...etc.

thanks! :-)

so modulation and secondary dominant are the same thing?

No, it has already been explained to you in the other topic

At most, a secondary dominant is a tonicization and it is not certain that it must necessarily lead to a modulation.

Now I understand better thanks; so it is a sort of momentary transition, where the tonic is no longer determined by the first degree of the scale in question, but by a different degree of the same scale... I believe

Practically it is a very brief modulation that only lasts for that moment, Clearly despite the A7 and D7, here you are clearly in C major

C+ (A7) D- (D7) G7 A-

Secondary dominants are V7 chords that create transient modulations.

so it's a very brief modulation to a secondary tonic?

If we wanted to analyze Gassy's example:

Gassy wrote:

Do+ (la7) re- (re7) sol7 la-

I V/II II V/V V VI

Fox wrote:

so it's a very brief modulation to a secondary tonic then?

Why do you feel the need to specify tonic? Maybe it's even another degree... it is what comes after in the case of modulation that decides it. But since it isn't a modulation, you can simply view it as a sort of harmonic punctuation (of C major in our example), analyzable as I wrote above.

Look at it this way, if it had happened:

C+ (A7) | D- (D7) | G7 C+ | A- (A7) | D7 E-

you would have

C major

I V7/II II V7/V V (which is the same as I I of G major) therefore then IV II V7/V7 VI specifically of G major

You see that the same chords have different functions and clearly, in my second example, it modulates to G major; modulation confirmed by other important degrees of the new tonality

specific tonic because from what I understand it temporarily tonicizes another chord of the key

automatically the V of II or the V of V, the V of VI etc. momentarily become the "new" tonic and therefore for example in the key of C Major the V of II is Am and Am will momentarily become (in a harmonic analysis) the I degree (that is to say the tonic of Am) ...I hope I'm not saying stupid things

it's just that I have many gaps

Fox wrote:

for ex. in the key of C major, the V of II is A major and A major will momentarily (in a
harmonic analysis) become the I degree (that is, the tonic of A major)

No. In that case, it is D minor that momentarily becomes the "tonic", i.e., I.

RedScharlach wrote:

No. It is actually D minor which momentarily becomes the "tonic", i.e., I.

Exactly... every degree of a key can temporarily be I, and be preceded by its V, which thus becomes a dominant seventh, even if it was originally of a different quality. Therefore, it is defined as a "secondary dominant". The VII is an exception, as there is no degree located a perfect fifth above it...