The principles of Indian classical music are well explained by these 40 principles put together by Pt Bhatkhande.

1. The Shuddha Saptak (The basic scale) is taken as Bilawal Thaat.
2. All the raags are divided based on the number of notes in the Aaroha and Avaroha as Audav (Raag of 5 Notes), Shadav (Raag of 6 notes), Sampoorna (Raag of 7 notes)
3. A raag cannot have less than 5 notes (out of 12 notes including komal and teevra)
4. The combination of Audav, Shadav, Sampoorna in the aaroha or avaroha make 9 types of raag based on the number of notes in it.
5. Each raag is based on a thaat, and has Aaroha, Avaroha, Vaadi, Samvaadi, Samay, Ras, Thaat.
6. A samvaadi is always fourth or fifth from the vaadi. If vaadi is in the poorvanga samvaadi will be in the uttarang and vice versa.
7. By changing the vaadi swar a morning raag can be changed into an evening raag.
8. To enhance the beauty of the raag a vivaadi note can be used very rarely.
9. Each raag has a vaadi. The raag is identified as a poorva raag or uttar raag based on the vaadi note.
10. Raags can be classified into 3 categories :
    • Raag with Komal Re, Komal Dha
    • Raags with Shuddha Re, Shuddha Dha
    • Raags with Komal Ga, Komal Ni
    Normally in the Pratah kaalin sandhi prakash raag, Re and Dha are never absent. And in Sayam kaalin sandhi prakash raag Ga and Ni are normally not absent.
11. Ma indicates whether the Raag will be sung at day time or at night.
12. The raags with Komal Ga, Ni are performed at afternoon or at mid night.
13. After the Sandhiprakaash raag mainly raags with Re, Ma, Dha, Ni shuddha are performed.
14. Sa, Ma, Pa are the important notes in raags of 3rd prahar of day and the night.
15. Teevra Ma is found mainly in Raags of the night. It's found rarely in the day time raags.
16. If the vaadi is one of Sa, Ma, Pa, that raag can be sung at all the times.
17. Ma and Pa can not be simultaneously absent from a raag.
18. Each raag must consist of the note Sa.
19. No two forms of the same note are taken one after the other in a raag. There are exceptions such as Raag Lalit though, to this rule.
20. The raag's beauty is enhanced more if sung at the designated time.
21. Teevra Ma and Komal Ni come together very few times.
22. The raags in which both the Ma appear are similar in nature. The aaroha is different but the avaroha is quite similar.
23. In the raags sung at 1st prahar of the night, and which have both the Ma, Shuddha Ma is taken in both aaroha as well as the avaroha but Teevra Ma is taken mainly in aaroha.
24. In raags of 1st prahar of the night aarohi Ni and avarohi Ga are Vakra. Ni in the avaroha is not emphasized.
25. In Indian classical music as opposed to the Karnatak classical music, the swar is more important than the Taal.
26. The poorva raag show their special characteristics in the aaroha, where as the uttar raag show their special characteristics in the avaroha.
27. Each thaat can produce poorva and uttar raags.
28. In the raags of the serious, calm nature Sa, Ma, Pa seem to have a prominent place. They are more effective in the Mandra Saptak. Whereas in the raags of light mood, this is not found to be so.
29. While entering from one thaat into another thaat, Para Mel Praveshak raags (raags on the border of the two thaats) are rendered.
30. The sequence normally followed is sandhi Prakash Raag then raags with Re Dha shuddha then the raags with Ga, Ni komal.
31. Sandhi Prakash Raag invoke Karun , Shant ras. The raags with Re, Ga , Dha shuddha invoke Shrungaar and Hassya ras. The raags with Komal Ga, Ni invoke Veer, Roudra Ras.
32. The raags which have Komal Ni normally have Shuddha Ni in the aaroha. For example Kaphi and Khamaj.
33. When two to four notes are together they cannot be called a raag . They can at best be called a taan.
34. In raag notes can be prominent, or insignificant (insignificant does not mean absent though).
35. After twelve at night and twelve in the morning Sa, Ma, Pa start assuming importance gradually.
36. In the raags sung in the afternoon, Aaroha either does not consist of Re and Dha or they are insignificant. In these Raags Ga and Ni really shine with full glory.
37. The raags with Sa, Ma, Pa as Vaadi are of serious nature.
38. In the dawn time raags Komal Re and Komal Dha are predominant and dusk time raags have the prominence of Shuddha Dha and Shuddha Ni.
39. The combination NiSa ReGa immediately establishes Dawn - Dusk time raag.
40. Poorva raags are more elaborate in the aaroha and uttar raags are more elaborate in the avaroha.