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2. 15-20.] Number, distinctions, and classification of the senses
The sense primarily useful for the journey of life is the knowing sense (jnanendriya), and the one capable of performing actions necessary for that journey—such as eating, moving, and seeing—is the acting sense (karmendriya).
For each of the five senses, there are two distinctions in terms of substance and nature. The material (pudgala) physical senses are considered substance senses (dravyendriya), while the spiritual results of the senses are referred to as nature senses (bhavendriya).
The substance senses can be classified into two types based on their functions and instruments. The senses that manifest as forms from the distinct composition of the pudgala skandhas (physical components) are called functional senses (nivritti-indriya), while the external and internal pudgala powers of the functional senses, without which knowledge cannot arise, are called instrumental senses (upakarana-indriya).
The nature senses also have two types: attainment (labdhi) and use (upayoga). The containment of knowledge obstruction (matijnana-avaraniya karma) or its eradication, which is a type of spiritual result, is referred to as the attainment sense (labdhi-indriya). The general and specific understanding of forms and other subjects that arises from the combination of labdhi, nivritti, and upakarana is called the use sense (upayoga-indriya). The use sense manifests in forms such as knowledge through thought (matijnana) and the sensory perceptions of sight (chakshu) and non-sight (achakshu).
The use of the nature senses refers to the ability to know formless (amurt) substances, but they cannot comprehend their comprehensive qualities and modifications; they can only know the modifications of touch, taste, smell, form, and sound.
Question: For each sense, we have found two distinctions in terms of substance and nature, and similarly, two types based on their functions and attributes. However, what is the sequence of their attainment?
Answer: The attainment sense must be established before any functional activity can occur. Without attainment, there can be no instrument; that is, once the attainment is achieved, then functioning, as well as use, can take place. Similarly, after achieving functional ability, use can occur, and once attainment of the instrument is achieved, then use can be realized. In summary, the sequential attainment of earlier senses leads to the attainment of later senses, but there is no rule that the later senses must be acquired only after the earlier senses.
Names of the senses: 1. Touch sense (tvak), 2. Taste sense (jihva), 3. Smell sense (nasika), 4. Eye sense (chakshu), 5. Hearing sense (shrotra). Each of the five senses has four types of attainment, function, instrument, and use.