what is "thaat"?

A thaat is a musical mode in Hindustani music which always has seven notes (excluding the repeated tonic) and is considered the basis for the system of organizing and classifying ragas in North Indian classical music. The notion of thaat, and the ten basic categories, were created by Pt. Vishnu Narayan Bhatkhande in the early decades of the twentieth century.

A thaat is a specific set of notes or swara. The idea for Thaat or mode originated in the Carnatic music tradition, where it was described as mela around 1640 A.D. by the musicologist Venkatamakhi. Bhatkhande visited many of the gharanas or traditions of Indian Classical music, and conducted a detailed analysis of the Indian Raga system, to come up with this set of ten thaats - this reflected a tradeoff between the degree of fit between a raga and its thaat, and the keeping the number of basic thaats small.

Each thaat contains a different combination of altered (vikrt) and natural (shuddha) notes. The flatting or sharping of pitches always occurs with reference to the interval pattern in Bilawal thaat. It is important to note that, as in the Western church modes, each thaat is a series of intervals, not a series of notes. That is, one can arbitrarily designate any pitch as Sa (the tonic) and build the series from there.

There are ten generally accepted thaats:
1. Bilawal (=Ionian mode): S R G m P D N S'
2. Khamaj (=Mixolydian mode): S R G m P D n S'
3. Kafi (=Dorian mode): S R g m P D n S'
4. Asavari (=Aeolian mode): S R g m P d n S'
5. Bhairavi (=Phrygian mode): S r g m P d n S'
6. Bhairav: S r G m P d N S'
7. Kalyan (=Lydian mode): S R G M P D N S'
8. Marwa: S r G M P D N S'
9. Poorvi: S r G M P d N S'
10. Todi: S r g M P d N S'

Bhatkhande applied the term thaat only to scales which fulfill the following rules:
1. A thaat must have seven notes
2. The notes must be in sequence S R G M P D N (whether suddh or vikrid position - both versions af a single note are not allowed
3. A thaat does not have separate ascending and descending lines (as do ragas)
4. A thaat has no emotional quality (ragas, by definition, have)
5. Thaats are named after a prominent raga in order to make then easy to remember