Where dynamics came from
How you shape the loudness of a phrase depends on when it was written. Three eras, three habits — and reading a piece in the wrong era's habit is one of the commonest ways to make old music sound wrong.
Baroque — terraced
The harpsichord and the organ physically cannot get gradually louder. So Baroque
composers — Bach, Handel, Vivaldi — wrote in blocks: a whole passage at one level, then a
step to another. f … then p … then f again. When a phrase is immediately repeated with
no marking, it's very often meant as an echo — the same notes, quieter.
Classical — graded, and speaking
By Mozart's time the orchestra could swell — the Mannheim court orchestra built its
fame on a long, unanimous crescendo (more on that below). But Classical composers used it
rhetorically, like punctuation: a sudden f answered by a p, an echo, a subito p
surprise. The dynamics talk — they follow the rise and fall of a spoken sentence.
Romantic — continuous
From Beethoven onward the whole dynamic surface is in motion — hairpins everywhere, long crescendos over dozens of bars, the volume never quite settling. Here is the Baroque phrase from the top, played the Romantic way:
Try it
Try
Take Twinkle's opening — the first phrase, then its repeat. Play it Baroque: the phrase
at f, the repeat as a clean echo at p. Then play it Romantic: one crescendo rising
across both statements. Same eight notes; listen to how completely the era changes what
they mean.
The usual mistake
Pouring Romantic hairpins over Bach and Handel — those phrases mostly hold one level and step to the next. And swelling a Classical crescendo into a big Romantic surge: in Mozart it's a short, speech-like inflection, over almost before you've noticed.