Rubato is widely regarded as a purely intuitive art. While it may be true that most performers rely solely on intuition for their rubato, a conscious approach may also be helpful. For the teacher of “analysis for performers,” a conscious approach is essential if rubato is to be discussed at all.
Rubato is a difficult subject to theorize. The late David Epstein made an admirable attempt in his book Shaping Time, using recordings by performers he admired to construct quantitative models. My approach here will be qualitative rather than quantitative, and introspective rather than empirical. Unlike Epstein, I will make no attempt to construct a general theory. Musicians in different times and places—even composers of the same generation, such as Chopin and Liszt—had distinctly different conceptions of rubato. One is probably justified, therefore, in approaching the idea of a general theory with caution.
Rothstein, William, "Like Falling off a Log: Rubato in Chopin's Prelude in Ab Major (op. 28, no. 17)" (2005). CUNY Academic Works.