What a thaat is
A thaat is a scale of seven swaras, in order, from Sa to Ni. Sa and Pa never change: they are achal, fixed. The other five can each take one of two forms: Re, Ga, Dha and Ni shuddh or komal (a semitone lower), Ma shuddh or tivra (a semitone higher). Two forms for each of five swaras make thirty-two possible scales.
Early in the twentieth century, Pandit Vishnu Narayan Bhatkhande chose ten of them and placed the raags he collected in whichever they drew their swaras from. A thaat is not itself a raag: it has no character, no phrases, no hour. It is the family a raag belongs to, and knowing it tells you at once which swaras the raag lives among.
The circle of thaats
Nine of the ten can be set in a ring, each a single swara from the next: the swara that changes is written on the line between them. The ring breaks once, between Bhairavi and Todi, where two swaras change; and Bhairav stands outside it, a swara from Purvi.
The ten
- KalyanTivra Ma · +1
- BilawalAll shuddha · 0
- KhamajKomal Ni · -1
- KafiKomal Ga and Ni · -2
- AsavariKomal Ga, Dha and Ni · -3
- BhairaviKomal Re, Ga, Dha and Ni · -4
- TodiKomal Re, Ga and Dha, tivra Ma · -2
- PurviKomal Re and Dha, tivra Ma · -1
- MarwaKomal Re, tivra Ma · 0
- BhairavKomal Re and Dha · -2
From light to dark
Count a step up for tivra Ma and a step down for each komal swara: Kalyan is the brightest, Bhairavi the darkest. It is only a way of hearing, but it is why a raag of Kalyan feels open and one of Bhairavi tender.
A raag's thaat
Many raags use fewer than seven swaras, and some use both forms of one: Bhatkhande placed each where its swaras and its character fitted best, and teachers sometimes disagree. Bhoopali, with neither Ma nor Ni, could belong to Bilawal as well as Kalyan; Bhatkhande put it in Kalyan, beside the raags it is kin to. A raag's thaat tells you where to begin, never all there is to know.