The topic of ‘softness of modes’ in Iranian music has been a source of discussion in music treatises from the scholastic and systematic periods until before the formation of the Dastgahi system. This issue, which was discussed under the title of the principles of softness, has not been widely discussed in existing sources of Iranian instrumental music. By examining the modes in contemporary instrumental music, it is possible to obtain common features in their structure and arrangement of intervals and consider them as the principles of softness in contemporary Iranian music. In this article, in order to find the principles of consonance in the of the Saba Radif, common features in the arrangement of the modes have been studied. Analysis of intervals such as tetrachords, pentachords and their relationship to the different modes have been studied so that they can be considered as an example of the current rules in Iranian classical music. It should be noted that Saba focused some Radifs specifically for three instruments: violin, santur, and setar. In this article, the modes of Saba's Radif are the set of modes found in the aforementioned . In fact, the Gusheh’s in these Radif are divided into three general categories: 1. Rhythmic, 2. Melodic, and 3. Modal. Modal Gusheh’s are the same as the modes, and they will be discussed in the present article. For this purpose, at the beginning, the types of Chahargan’s and Panjgan’s, or tetrachords and pentachords, or as they were called in ancient Iranian music, Zel-Arba’ and Zel-Khams, in the Saba Radifs are specified. Then, the method of combining these tetrachords and pentachords, which potentially provide a range of one octave for presenting a mode, is discussed.
The results of this research show that the Saba Radif consists of 72 modes, which are formed by combining 9 tetrachords and 9 pentachords in 22 different types. Each of the modes in the Dastgah and Avaz of the Saba Radif is considered in the range of one octave, which is formed by combining one tetrachord and one pentachord. The Shahed tone is also considered in the common tone between the connected tetrachords and pentachords. Each of the tetrachords and pentachords is made up of specific Lahni intervals. The term "Lahni intervals" refers to connected intervals or secondary intervals with different qualities. The reason for naming these intervals is the continuity of their intervals. In ancient treatises on Iranian music, the word "Lahn" was a specialized term in music, and its meaning can be considered equivalent to the concept of melody in contemporary music. This shows that in ancient Iranian music, as in today's Dastgahi music, the most important intervals for creating melody or Lahn were connected intervals. The mentioned tetrachords and pentachords are divided into three parts: 1. Zalzali 2. Tanini and 3. Mostazad, each part includes three subgroups. The tetrachords and pentachords of the Zalzali include: 1. Tork, 2. Shur, and 3. Segah. The tetrachords and pentachords of the Tanini include: 1. Mahur, 2. Nava, and 3. Dashti. The tetrachords and pentachords of the Mostazad include: 1. Chahargah, 2. Mokhalef, and 3. Zabol. By combining these tetrachords and pentachords, a total of 162 modes can be formed, of which 22 combinations have been used and 140 other combinations remain as potential. Of these 140 potential combinations, 63 do not comply with the criteria for minimum consonances in the modes in this Radif, which is the presence of at least 5 consonant ratios and a maximum of three single tones in a mode, and will be considered dissonant. However, there are 77 other potential combinations that are in accordance with the aforementioned criteria, and their acceptance in modulations or as new modes seems likely to the contemporary listener. Because of this, the role of the Shahed tone, which has the most important role among the tones of a mode, is clear in these potential modes. There will be a great potential for implementing these modes and applying the results of this article. In addition, just as 72 modes are formed from 22 combinations of tetrachords and pentachords in this Radif, it is possible to create more than one mode from one type of combination by changing other important tones, such as the 1st tone. Apart from the criterion of having at least 5 consonant ratios and a maximum of 3 single tones in consonant or semi-consonant modes, there are 4 other criteria in tetrachords, pentachords, and consonant and semi-consonant modes, which are: 1. No succession of two Baghiyeh intervals, 2. No succession of more than two Mojannab intervals, 3. No succession of more than two Tanini intervals, and 4. Succession of the Mostazad and Baghiyeh intervals. These principles existed in Iranian music in the 7th century AH as well, and Safi al-Din Ormavi mentioned some of them in his book Advar. In general, it can be said that the principles and criteria of consonances in Iranian music have not changed significantly from the 7th century to the .