Lessons and Instructions from the Tamil Siddhas
T.N. Ganapathy wrote a great book called The Philosophy of the Tamil Siddhas, which explains about this Indian cultivation tradition.
Siddhas are yogis who continue to live in the world, in their body, after self-realization. They are beings who have achieved enlightenment, the Tao, and achieved the nirvana of no more sorrow and suffering.
In the Indian tradition we generally have Natha Siddhas, Rasa Siddhas, Mahesvara Siddhas and Sangata Siddhas.
They all practice various yogic methods to attain enlightenment that involve meditation and sexual continence. This leads to the arising of kundalini and physical/chi purification, and then higher stages of spiritual progress.
The stages of cultivation practice according to the Tamil Siddhas first involve the unripe physical body, or stuha deha. This is the gross human form, or form skandha of Buddhism. You can use hath a yoga and other purificatory process to help cultivate and purify the human physical body.
If one cultivates well enough to cause one’s yang chi (kundalini) to arise and clear one’s chi channels, one can then achieve the “perfect body” or siddha deha. This is akin to opening all the chi channels within your body and achieving the yin shen of Taoism, illusory body of Tibetan Buddhism, and mind-born body of Buddhism. In Tibetan Buddhism the illusory body is also known as a deity body, or divine body composed of chi. In Hinduism this would be the pranamayakosha (etheric body) of the five koshas.
The siddha deha can do and be anything at the will of the owner, and has free movement in the universe (depending upon the stage of accomplishment). You cultivate it as a result of yoga, but its attainment requires the stage of kundalini shakti. To attain it, you must cultivate the inner vitality of the body, through various methods such as nei-gong internal energy work, which is why all yogis in every cultivation school cultivate sexual restraint. After its attainment you can gain some degree of superpowers if you bother to cultivate them.
Basically, all you need to know is that the kundalini yoga processes lead to the attainment of the siddha deha. This achievement, however, is not enlightenment. However, the achievement often gives rise to the attainment of various superpowers, or siddhis, and many yoga practitioners therefore mistakenly stop at this stage.
These things are described in the Surangama Sutra of Buddhism where Shakyamuni Buddha describes how one can win freedom from the sensation skandha and can then develop various superpowers connected with the conception skandha.
After the siddha deha achievement, the Tamil Siddhas say that the next stage of progress is to achieve the mantra deva, or pranava tanu, which is free from all gross matter and all impurities. That means it transcends the gross physical body and subtle chi body, or deity body (siddha deha achievement).
From this description, this is probably the Causal body of Vedanta - the conception skandha equivalent in Buddhism. It is said to be a body of sound, which we might interpret as having to do with movement or active consciousness (a connotation that once again suggests the conception skandha of mentation). In Hinduism this would likely correspond to the manamayakosha (mind body) of the five koshas.
The other alternative is that it refers to the “I am” impulse within the True Self, equivalent tot he seventh consciousness soy Buddhism. This is the volition skandha of Buddhism, the afflicted mind that is a perturbation on pure consciousness. The siddha deha is sometimes called the AUM body, which is often called “I am,” so this correspondence may hold too. After one gives up the self-notion, they can become the true absolute nature.
These are all achievements on the way to the sambhogakaya attainment of Buddhism, but this is not necessarily that attainment yet.
The pranava tanu as a cultivation foundation can eventually result in the attainment of an eternal spiritual body, called the jnana deha or divya tanu (divya deha). This body is said to be eternal, indestructible and everlasting. Anyone who attains this attains Sivahood. The aspirant who achieves this is called a jivamukta, and becomes one with the witness of the universe. One identifies themselves with universal life at this stage, and their body is said to be a vast expanse without determination, which probably refers to borderless awareness or infinite pure consciousness rather than a “body” of any type (though you can call that a body). This is probably the dharmakaya of Buddhism.
In any case, according to the Tamil sequence of progress (and there are differences from this or that Tamil school or scripture), when one achieves the divya deha, or body without form that is like a body of light, one attains enlightenment. In this case “Light” does not mean photons or illumination but clarity like an empty clear mind.
The great thing about this simple description is that one can find matches with Buddhism, Vedanta, and Taoism. The spiritual road is that everyone must cultivate to free themselves from the form and sensation skandhas, or physical and subtle bodies, but this is not enlightenment. However, this results in the attainment of the yin shen of Taoism and mind-born body of Buddhism, or the illusory body of Tibetan Buddhism. Then a yogi-aspirant must free themselves from the personal mind of conceptions, or conception skandha, which is akin to the causal body of Vedanta and manamayakosha. That means they can attain the stages of samadhi/dhyana that involve mental emptiness. After this one still must free themselves from the volition and consciousness skandhas of Buddhism, and Supra-Causal body of Vedanta so as to attain the absolute nature, or perfect enlightenment. This is when one finds their true self-nature, which means that they discover their True Self.
You can also find correspondences to these bodies, and this overall progression scheme, in terms of the five sheaths of Hinduism: the annamayakosha (food body), pranamayakosha (etheric body), manamayakosha (mind body), the vijnanamayakosha (wisdom body), and anandamayakosha (bliss body).
The Tamil Yogic path is basically the same path as everyone else’s with the warning that superpowers are not the Tao or enlightenment, and any bodies are not the Tao or enlightenment. However, along the way to enlightenment one attains more purified bodies of enjoyment/bliss, but the supreme nature is bodiless.
It would be useful to study these various correspondences in order to prove, one again, that the spiritual path is one, non-denominational yet described differently by different schools.