In the classical music world, feeling or “expression” is a thing to be learned. In the traditional music world, feeling just is the music. Although this is a simplistic reduction, it is true!
For the adult fiddle/violin student, understanding this basic difference in music-style requirements can help you choose your balance between classical and traditional (non-classical) in your learning plan.
In its compositional design and expected performance style, classical music requires a technical skill-set to create the sounds and nuanced effects which are the core of the classical music sound. There are many subsets of style under the term "classical." The player creates the expression of the music, which can change from one moment to the next, and can require pyrotechnical gymnastics and high-precision control.
Fortunately, there is a huge wealth of “classical” music accessible to the beginner/intermediate student which requires only a few technical skills, and this is where most adult learners are happy and satisfied. To go significantly further may require an exponential effort, which is a several-years-long commitment.
In traditional music, tunes – jigs, reels, polkas, waltzes, and so on – are the forms of this style rather than the symphonies, sonatas, concertos etc. of classical music.
To get an idea of this, check out thesession.org. Most are dance tunes. As such, they are usually learned in a rigid and predictable tempo and pulse/groove. There is a defined phrasing for each type of tune which all good trad players respect.
The “expression” of a trad tune is built into the way it is designed. A player fits/merges into a tune and has very little to create musically because it is already there.
For traditional forms with slower tempos, such as aires and waltzes, a simple approach always sounds good but expression may be more personal and skillful.
With traditional music, the (bow) sound quality can be intense or gentle, but a “curated” or nuanced sound is not required. Players evolve with their own unique sound – and also left hand technique – which is not based on advanced technical skills. Trad tune difficulty ranges from absolutely elementary to borderline pyrotechnical, and there are dozens – even hundreds – of tunes at every skill level.
All music yearns to be expressed with feeling. Knowing the unique routes that classical and traditional music take to that destination can help every player choose the path that best suits their inner musician.