About Ragas Poorvi and Puria Dhanashri.

     Raga Poorvi is an Ashrya Raga of Poorvi Thaat and also a Raganga Raga under Raganga Paddhati. Puria Dhanashri is also classified under Poorvi Thaat and is a Raganga Raga of Poorvi. Here I have not dealt with the description of these Ragas, but with the basic difference and similarities between these Ragas
Similarities;  (i) Both are classified under Poorvi That.   (ii) Both have Rishav and Dhaiwat swaras as Komal ( r , d )  (iii) Both are Sandhiprakash Ragas ( sung during dusk hour)
Dissimilarities:   
(i)   The main differentiating factor in these Ragas is the use of Shuddha Madhyam (m) and its chalan in Poorvi, which is a  'varjit' swara in Pooria Dhanashri. 'm' is used in a special way in Poorvi   i.e. G M rm G, r G M P M G m r G,  P, dMP- M G m rG. This note pattern is to be mastered under the guidance of a Guru, Otherwise while pronouncing P M G m G , Raag Bihag or Paraj will appear. (This can not be explained in words).   Similarly  pronouncing of  - r' N d P, M r G,  d G P,  d M G r S- in Pooria Dhanashri should also be learnt under guidance of a Guru.
(ii)   Vadi and samvadi are different. In Poorvi they are G and N,  and In Puria Dhanashri they are P and r.
(iii) Under Vishnu Digamber Paddhati , Pt. O.N Thakur has classifed both the Ragas as Shadav-Sampoorna, whereas Pt.Vinayak Rao Patwardhan has classified Poorvi as Shadav-Sampoorna (P varjit in aaroha) and Puria Dhanashri as sampoorna.
     In his treatise "Sangeetanjali" Pt.O.N.Thakur has stated that to avoid Puria Dhanashri creeping in while singing Poorvi, one should never use the swara pattern M G M r G and while doing avaroha  r' N d P  and N r' N d P should be avoided .  Similarly swara patterns - S r 'N ,  'N S r 'N,  S r S r 'N - should not be used to stay at 'n, which will invoke Gauri Raga.
     Other 'tips' given to differentiate the Ragas are:-  (i) Shuddha Madhyam (m) should never be used in Puria Dhanashri. (ii) N to be  used less in Puria Dhanashri as compared to Poorvi.  (iii) while singing Puria Dhanashri P should be made more prominent than G, although G is a nyas swaraa the Raga.. Similarly in Poorvi G has to be given prominence.  (iv) Pt Bhatkhande has stressed that Poorvi is invoked  immediately  by use of 'N , S r G, m G and has also termed it  as a 'Pakad' (catch phrase) of the Raga..Many bandishes in Poorvi start with this phrase and is used extensively in other places also in the bandishes.. This note pattern is not used in Puria Dhanashri, which uses note pattern 'N r g instead.