A raga is best understood not as a fixed melody but as a detailed set of rules and possibilities a performer works within, specifying which notes belong to the raga, how the melody characteristically ascends and descends, which notes function as the raga's most important resting points, and which specific melodic phrases and ornamentations are idiomatic to that raga and not to others sharing the same basic set of notes. Two ragas can, in principle, share an identical scale and still sound entirely distinct in performance because of these differences in characteristic phrasing, emphasis and ornament, a distinction that separates raga based music sharply from the Western idea of a scale as simply an ordered set of pitches with no built in melodic personality of its own.
Hindustani music of North India and Carnatic music of South India each maintain extensive, only partly overlapping systems for classifying and naming ragas, Hindustani theory generally organizing ragas into ten parent scale groupings called thaats and Carnatic theory using a more systematically exhaustive scheme of seventy two parent scales, melakarta, from which further derived ragas are generated, reflecting two related but independently theorized approaches to the same underlying musical concept. A trained performer improvises extensively within a chosen raga's rules during a performance, so no two renditions of the same raga, even by the same musician, are ever identical, even though a knowledgeable listener can recognize the raga's distinct identity across many different specific performances.