The Main Characteristics of Romantic Music
Freedom of form and design. It was more personal and emotional.
Song-like melodies (lyrical), as well as many chromatic harmonies and
Dramatic contrasts of dynamics and pitch.
Big orchestras, due mainly to brass and the invention of the valve.
Wide variety of pieces (i.e. songs up to five hour Wagner operas)
Programme music (music that tells a story)
Shape was brought to work through the use of recurring themes.
Great technical virtuosity.
Nationalism (a reaction against German influence)
Postromantic (Blair Allen Johnston - the dissertation of your link)
Deformation and Structural Tension
Hyperdissonance: Definition and Initial Analytic Applications
Formalizing the Model: Tension Arcs
Exaggeration of Tonal Premises
Distortion of Tonal Premises
A Parenthesis: Neutralization of Tonal Premises
I don't fully understand what he's saying, in terms of chromatic expansion, elaborations of linear tonal syntax, exaggeration and fragmentation of tonal syntax and the superimposition of conventional functional tonal structures and intense chromatic and modal structures.
Let's assume that if someone will be able to find and read this dissertation he will know or understand what is meant by chromatic extension.*1)
So let's pick another example...
However, the Encyclopædia Britannica provides a
[A] musical style typical of the last decades of the 19th century and first decades of the 20th century and characterized by exaggeration of certain elements of the musical Romanticism of the 19th century. Postromanticism exhibits extreme
largeness of scope and design, a mixture of various musical forms (e.g., opera
and symphony), and heightened contrapuntal complexity (i.e., a long or vast
array, or both, of simultaneous but independent musical lines or events). Often
Postromanticism also embraces vivid religious or mystical fervour, a sense of
longing, and a sense of the grim and the grotesque.
Exaggeration and fragmentation of tonal syntax
“Exaggeration” and “vast array…of simultaneous but independent musical lines
or events” are particularly telling. From them, I offer a more specific observation: if the
Romantic is characterized by chromatic expansion and the development of striking
elaborations of linear tonal syntax, then the Postromantic is characterized by exaggeration
and ultimately fragmentation of tonal syntax, and the juxtaposition or superimposition of
conventional functional tonal structures and intense chromatic and/or modal structures
that challenge and even deform the functional tonal basis. In my view, complex
interaction of variegated melodic-harmonic components is one source of the continuing
fascination Postromantic music holds.
A basic claim in the present document is that Rachmaninoff was a Postromantic
composer, not an anachronistic Romantic composer.
To describe the development of harmony from basic chords to diminished seventh chords, mediant, neapolitan 6th, Italian-, French- and German-Sixth until the Tristan chord would be a theme too vast to answer the chromatic extensions.
The best advice would be to listen to the music of Rachmaninoff and analyze his chords and progressions. (Just the intro of his Piano concerto will provide us a full range of interesting harmony!)