Purva (also called Purvya) belongs to a cluster of ragas bearing a family resemblance to raga Puriya in terms of swara material, and phraseology, melodic center of gravity, and therefore aural impression.
Puriya: S r G M^ D N
Puriya-Dhanashree: S r G M^ P d N
Poorvi: S r G M M^ P d N
Puriya-Kalyan/Purva: S r G M^ P D N
What is common to all of them is komal (flat) Re, shuddha (natural) G, tivra (sharp) Ma, and shuddha (natural) Ni.
At the commencement of a concert at Los Angeles CA in 1991, Ustad Vilayat Khan introduced Purva with its ascent and descent.
Ascent: N r G M^ D N r' G'
Descent: r' S' N D P M^ G M^ r G N. r S
In a tape-recorded interview after the concert, the Ustad says that Purva is the same as the raga commonly known as Puriya Kalyan. He also argues that Purva is the right name for this raga and Puriya Kalyan is misleading because there is no trace of the characteristic Kalyan element in Puriya Kalyan. Although he does not identify the "characteristic Kalyan element", he probably considers the shuddha (natural) Re swara as essential for the Kalyan classification. If this is his argument, it has some validity.
Kalyan is a family of post-sunset ragas, which should use the shuddha (natural) Re swara. The komal (flat) Re of the Puriya cluster defines Purva as a "sandhi-prakash" (twilight zone, in this case, sunset-hour) raga. By this logic, Puriya Kalyan cannot be classified with the Kalyan family.
With these observations, Ustad Vilayat Khan has raised the issue: Are Purva and Puriya Kalyan two different ragas, or two names for the same raga?
Musicologist VN Bhatkhande looked at this issue in the 1940's, when Purva was a mature raga, and Puriya Kalyan had just begun to gain acceptance. Based on textual evidence, but very limited exposure to performances of Puriya Kalyan, Bhatkhande concluded that they are, indeed, different ragas. (Bhatkhande Sangeet Shastra. Vol.III, Ed.LN Garg, Sangeet Karyalaya Hathras, third edition, 1984. Pgs. 251-254)
Genealogically, Bhatkhande connects Puriya Kalyan to raga Purva Kalyan of the Gamanashram parent scale in the Carnatic (South Indian) tradition, which has identical swara material, and near-identical scale. Purva, on the other hand, he attributes to a combination of Poorvi, Maru and Gaura.(Ibid)
During the review of this recording, Ustad Vilayat Khan described Purva as Puriya with a Pa added to it,or Puriya Dhanashree with a shuddha (natural) Dh swara replacing the komal (flat) Dh. Therefore, it appears that the Ustad saw Purva clearly as a member of the Puriya cluster. However, it is also possible to interpret the same scale as Yaman with a komal (flat) Re replacing the shuddha (natural) Re. And, this may very well explain why the Carnatic nomenclature of this scale associates the raga with Kalyan (Yaman).
Thus, Ustad Vilayat Khan plays Puriya with a Pa and calls it Purva. And, Puriya Kalyan specialists perform a raga to the same scale, probably conceived as Yaman with a komal (flat) Re. What is the difference ?
To explore this issue, we can compare Vilayat Khan's Purva with the Puriya Kalyan of its most popular exponent, Pt. Bhimsen Joshi (Music Today: A:97009).
The most obvious conclusion is that neither Purva of Vilayat Khan, nor Puriya Kalyan of Bhimsen Joshi can escape the aural images of either Puriya or Yaman. Both the maestros also use the suppressed micro-swara of the komal (flat) Re characteristic of Puriya. A detailed examination of their respective phraseologies also fails to identify any distinctive phrase that one of them uses, and the other does not.
However, the aural experience they create is distinctive. Purva does, indeed, come through as closer to Puriya, and Puriya Kalyan does emerge as being inspired more by Yaman. The secret probably lies in the probabilistic technique of raga differentiation.
If you play Yaman with a komal (flat) Re, the ascent becomes pure Puriya anyway, while the descent remains Yaman until it reaches Ga, and returns to Puriya below it. Thus, if more phrases are ascending, and fewer are descending, Puriya dominates the aural experience. And, vice versa.
The second aspect of this same probabilistic technique is how much melodic development is done in the mid-octave region, where the Yaman flavor is dominant. If you de-emphasize the melodic development in the mid-octave region, Puriya can dominate the aural experience. And, vice versa.
The third facet of this technique is the use of multiple phraseologies. If you use the Puriya descent in the upper tetrachord (N-D-M^) in addition to the Yaman descent (N-D-P), and do so often enough, Puriya dominates. By the same logic, if you use the Yaman-type ascent in the lower tetrachord (N-r-G-M^-P) in addition to the Puriya ascent (N-r-G or N-r-M^-G), and do so often enough, the Yaman flavor dominates.
Allied to this approach is the inclusion/ exclusion technique of raga differentiation. If the Yaman flavor surfaces in the mid-octave region, it is possible to highlight the Yaman angle, or balance the two, by including the mid-octave region in a majority of phrases. This means using a phraseology, on an average, of broader melodic spans. Conversely,the Puriya facet is more easily isolated, by using phrases, on an average, of shorter melodic spans so that the mid-octave region can be excluded, when desired.
The probabilistic technique of raga differentiation is the most subtle and advanced of all melodic disciplines. On the basis of permissible phraseologies, the two ragas are identical. The only technique for differentiating them is through differential weightages given to different segments of the octave.
It is difficult for two ragas of such subtle differentiation to co-exist with anything like comparable circulation or popularity. It is a different matter – though not entirely irrelevant – that even audiences of considerable cultivation would find the differences imperceptible. Consequently, it appears that Puriya Kalyan, with the commonly understood Yaman as its reference point, has remained in circulation. And, Purva, with the more profound Puriya reference point, is now rarely heard.
This point of view is at variance with contemporary scholars and learned musicians, including Ustad Vilayat Khan, who regard Purva as the original name for the present-day Puriya Kalyan. The debate can continue.