Pandit Vishnu Narayan Bhatkhande (1860-1936) who was one of the most influential musicologist of North Indian Classical Music has created the Thaat System. He introduced 10 basic thaas in North Indian Classical Music. As per him, each raga is based on or a variation of one of these 10 thaats. These thaats are as follow:
- Purvi/ Poorvi
Each raag is based on one of these several thaats. As per Pandit Bhatkhande only those scales that follow the below mentioned rules will be considered as Thaat-
- A Thaat must have 7 swars out of 12 swars (7 Shudh, 4 Komal and 1 Tivra)
- The swars must be in ascending order (Sa re ga ma pa dha ni)
- Whether Shudh or altered, both versions of a single swar are not allowed.
- Unlike Raga, a Thaat does not have separate ascending or descending orders.
- A Thaat does not have any emotional quality which the ragas have.
- Thaats are not sung but the ragas derived from the thaats are sung.
Bhatkahande ji named his Thaats after the most important ragas that were associated with that Thaat. For e.g. Asavari was named after its prominent raag Asavari. Similarly Kafi after raag Kafi, Bhairav after raag Bhairav etc.