Classification of Raagas has been in existence since the phase when Indian music had got its importance and recognition worldwide. With time, the raagas were classified further. In the thirteenth-century, the total number of raagas had increased to 264 and modern scholars have not yet been able to reconstruct these raagas satisfactorily, in spite of the fact that a rudimentary form of notation, based on the Indian equivalent of the Western tonic sol-fa, was given by both Jsarngadeva and Matanga.

The basic difficulty lies in the interpretation of the intervals used in each of the raaga. Present-day Indian classical music is normally accompanied by a drone which establishes the tonic or ground-note quite clearly. In modern music the ground-note remains unchanged from one raaga to the next and changes of scale are achieved by using vikrita svaras (‘altered notes’) i.e. flats and sharps. In the jati system, however, scale changes were achieved by shifting the ground-note to different points of the two parent scales. Only two altered notes, kakalini and antaraga, were used, apparently serving as leading notes, and these were used only in ascent. In ancient India, music was classified in terms of raagas (masculine), and their wives, called ragini, which was sometimes expanded to include putras (their sons) and bharyas (wives of sons).

In the beginning about the sixteenth century, a new system of classifying raagas in terms of scales was introduced. These scales are called mela in south India and that in north India. Since no musicologist of the past gave any convincing and rational explanation for the prescribing the raga-time association, it was left to Pandit Vishnu Narayan Bhatkhande to explain the rules on this subject generally observed by Hindustani musicians. A day of 24 hours is divided into two - the diurnal and nocturnal halves. Of these, the ‘Dinegeya’ or ‘Suryamsa raagas’ (diurnal) are rendered during the day, and the ‘Ratrigeya’ or the ‘Chandramsa raagas’ are rendered during the night. The time punctuating the finish of day and the commencement of night is ‘sandhi’, and the raagas of this hour are called the ‘Sandhiprakash raagas’ or the raagas rendered during the twilight time; while those sung at the conclusion of night and the beginning of morning are called ‘Pratah-sandhi raagas’.

The day is divided into eight praharas or quarters or watches, each lasting for three hours. Of the eight praharas, five belong to the day and the other three to the night. The raagas in each of these praharas are classified on the basis of the notes prominent in each. There are some empirical rules of the thumb framed by Pandit Bhatkhande with regard to the assignation of raagas to the various praharas. Those raagas whose stress falls on the lower tetrachord (poorvanga) - from ‘sa’ to ‘pa’ - are to be rendered during the late afternoon, early evening and the early part of the night. While those in which the upper tetrachord (uttaranga) - from ‘ma’ to ‘sa’ - is stressed, are rendered during the last watch of the night, past midnight, and also the wee hours of morning. The break of day starts off the first watch.

Mela and that are considered as the theoretical devices for the classification of ragas in Indian music. Raagas may be heptatonic (sampurna), hexatonic (shadava), or pentatonic (audava). They have certain scalar elements; for example all raagas have specified movements which enable the melody line of the raaga to be carried from one octave to another, the ascending movement being called ‘droha’ (drohana) and the descending movement, ‘avaroha’ (avarohana). In contrast to scales, however, which are step-by-step arrangements of notes, raagas generally involve omissions of specific notes (varjva svara) and zigzag movements (vakratva), which are also usually specified. Nor are raagas slaves to scales, since accidentals are commonly used in many raagas, and in raagas such as the north Indian Bhairavi and Pilu all rive accidentals are permitted. A further distinction between scale and raaga is found in the varying emphasis placed on the different notes, which is characteristic of each raaga. In this connection, the term ‘vacli’ or ‘jiva-svara’ refers to the most prominent note of a raaga, and ‘samvadi’ to the second most prominent note. The terms ‘vadi’ and ‘samvadi’ were used in early Indian music to refer to the sonant and the consonant. In modern times, however, the ‘samvadi’ is not always consonant to the ‘vadi’.

Raagas, however, also have melodic elements and are generally recognized by what are called ‘catch’ phrases (pakar or raktiprayoga). Many raagas also have characteristic ornaments associated with certain notes, and these are further identifying features. In north Indian music one sees the beginnings of a different method of raaga classification based on these melodic elements, where a number of raagas which have certain phrases in common are given generic names, such as Kalyan, Malhar, and Kanhra, with specific names used to distinguish the various raagas within the same genus. This is, however, a secondary means of classification and has not been fully developed.

To illustrate the difference between raaga and scale, a musical example gives some characteristic phrases in six north Indian raagas which are traditionally described.

The pre-dawn watch, which begins at 3 a.m. and lasts until 6 a.m., is the time for the raagas in which komal rishabh and, at times, komal dhaivat appear prominently. These are uttaranga-dominated raagas. The emphasis on the upper tetrachord during the waking hours could be interpreted to signify the note of longing for light or summons to prayer. The raagas also symbolically connote the convergence of light and darkness, sleep and wakefulness, associated with the brahma-muhurta, for example, Sohini, Lalit, Bhatiyar, Kalingda.

The first prahara of the day begins at 6 a.m. and ends at 9 a.m. This is the time for those raagas in which komal rishabh and komal dhaivat occurs along with shuddh rishabh and dhaivat, for example, Bhairav, Ahir Bhairav, Ramkali, Gunakali and Bhairavi, the various forms of Todi like Mian ki Todi, Deshi Todi, Bilaskhani Todi and the Bilawal group of raagas like Allaiya Bilawal, Devgiri Bilawal. There is a palpable devotional awe and a ‘prayerful’ note in many of these raagas, especially in the Todi and the Bhairav groups when they are being elaborated in the lower register in slow tempo. The well-known bandishes in these raagas reinforce this characteristic.

The second prahara of the day lasts from 9 a.m. to noon. Many of the morning raagas sung at this time figure in the first prahara, so the note configuration stays the same. The late morning raagas such as Jaunpuri as also the Asavari and the Bilawal group of raagas are rendered during this time. Also figuring in this watch are Deshkar and Sughrai. The sun is, at this point of time, luminously prominent and thus raagas like Jaunpuri and the Bilawal group brim with the hectic activity and radiant energy associated with the intensification of the sun on the horizon.

The third prahara lasts from noon to 3 p.m. Raagas in this watch accentuate komal rishabh, komal gandhar or komal nishad, example, the raagas belonging to the Sarang group - Brindavani Sarabg, Shuddh Saarng and Gaud Sarang. There is an atmosphere of iridescent lushness about these raagas, evoking at once the cool splendour of a bower or the shade of bunches of broad-branched tress on a hot noon. It is worth noting that the number of raagas rendered during this prahara come down significantly, given that activities wind down during this time of the day with soaring temperatures.

The fourth prahara and concluding portion of the day lasts from 3 p.m. to 6-7 p.m. The late-afternoon raagas belonging to this group like Bhimpalas, Dhani, Patdeep, Dhanashri and Multani stress komal gandhar or komal nishad. These raagas are generally rendered before 5 p.m. They are languidly sensuous raagas, especially Bhimpalas, evoking the pleasurable and sated atmosphere of a late-afternoon siesta at a time when the sun is at its peak. The appearance of tivra madhyam in Multani signals the entry of early dusk. The ardent agitation and restlessness of the raaga evokes the anxiety related to the setting of the sun and the slow fading of light.

The raagas sung after 5 p.m. until before 7 p.m., the time of sundown, are called the sandhiprakash raagas. They have the same note configuration as the raagas occurring in the first prahara; the only difference is the emergence of the tivra madhyam along with komal rishabh and komal dhaivat, as in Marwa, Shree, Poorva, Jaitashri amd Poorvi. The setting of the sun, the fading of light and the anticipation of darkness bring the mind, as with dawn raagas, once again to the transitional zone between light and darkness. The raagas of this period convey, as with all sandhiprakash raagas, conflicting emotions related to restless yearning and contemplative quiet.

The first prahara of the night begins around 7 p.m. and lasts until 9 p.m. The raagas of this watch have shuddh dhaivat, rishabh and gandhar. All raagas belonging to the Kalyan group occur in this watch, example, Yaman, Shuddh Kalyan, Shyam Kalyan, Chayanat, Bhoopali, Hamir and Kedar. These raagas emanate an atmosphere of sense of serene bliss, associated with the winding down of the day’s activities.

The second prahara of the night begins at 9 p.m. and ends at midnight. The raagas of this watch have komal nishad and komal gandhar, example, Jaijaiwanti, Bihag, Shankara, Durga, Baheshri, rageshri. The raagas of this quarter radiate the enchanting darkness and the radiant amorousness associated with the early and later part of night. A good number of raagas in this group are `romantic` in ambience and import.

The third and last prahara of the night lasts from midnight until 3 a.m. The raagas in this slot use the same notes as those in the previous one. Some of the deep, expansive and majestic raagas of the night like Darbari, Malkauns, kaushi Kanada and other forms of Kanada come in this watch. These raagas emanate the enigma of the deep blue stretches of nocturnal darkness, the hush and the grandeur of cosmic vastness.

Both the morning and the early evening raagas share a fairly identical combination of notes. The major difference is that the morning raagas use shuddh madhyam, while the sandhiprakash raagas of the evening use tivra madhyam.

Besides the time-bound raagas, there are raagas associated with seasons. But unlike the time-bound raagas, the seasonal associations are not so rigidly adhered to. Basant and Bahar, the raagas associated with spring, and the Malhar group associated with monsoon, can be sung during the second prahara of the night. Raagas like Desh and Maand enjoy a flexible temporality. Though a morning raaga, Bhairavi usually forms the concluding piece in a late evening concert. Here precedence wins over habit.