The term Siddha is related to the word siddhi, which signifies the experience of Siva. Siddhisvara (Lord of the Siddhis) is one of the names of Siva. Siddhis indicate that the practitioner of Yoga has attained a stage of inner development that allows him to reach the ultimate goal, namely, liberation. It is wrong to think that the Siddhas are magicians or uncouth ascetics credited with supernatural powers. Nor are they atheists or agnostics, as is commonly believed. They believe in God, but not a God of this or that religion. For most of them there is a God, Siva, without any limitation or attributes. Siva is grammatically and philosophically an impersonal conception. The real name for Siva is "It" (or atu), "Thatness," or "Suchness." A genuine Siddha is beyond atheism and faith (theism) alike.
Nine main Siddhis
According to the Tamil Lexicon siddhi means "realization," "success," "attainment," "final liberation." A siddhi is an accomplishment on the psychic plane. Siddhi may also mean mysticism in Tamil. In the Tevaram siddhi means "success" in attaining God. The real meaning of the word siddhi best expressed by word such as "attainment," or "accomplishment" connected with the super physical words. In Zen buddhism we come across the term satori, which may be translated as "enlightenment." which is very near to the Hindu concept of siddhi amounts to an actual surpassing of human condition and may be likened to an "ontological mutation." In the words of Mircea Eliade, by attaining siddhi, "one is trying to break down the structures of the profane sensibility" to make way for extra sensory perception as well as an unbelievable control over the body. A siddhi, in short, is an effort directed to the "death of profane man" and a state of consciousness cosmic in structure.
Traditionally siddhis are eight in number, known as asta siddhi. Asta siddhi is of three orders, two siddhis of knowledge (garima and prakamya), three siddhis of power (isitva, vasitva, and kamavasayitva), and three siddhis of the body (anima, mahima, and laghima). The Hindu thpught generally recognizes eight siddhis, though occasionally eighteen and twenty - four siddhis are also acknowledged. In the Uddhava Gita twenty-three siddhis are enumerated. The Tirumantiram speaks to sixty-four siddhis. In Patahjal's Yoga Sutra, sixty-eight siddhis are classified. In Jnanavettiyam-1500 and in agastiyar Jnanakaviyam-1000 mention is made of sixty-four siddhis. Verse 337 of bogar Karpam-300 speaks of eighty-four siddhis. Saint Ramalinga Swamigal also says that there are sixty-four siddhis. In the Yogatattva Upanisad we find certain details about siddhis. In Tamil literature a list of the siddhis is to be found in Parajoti's Tiruvilaiyadar Puranam, in Tayumanavar's Tejomayanandam, and in Siddharganam, in Pambatticcittar's songs, in Saint Ramalingam's Tiruvarutpa, and in Tirumular's Tirumantiram. It is said that one who has attainted siddhi "can hear the grass as it grows." Pambatticcittar and Tayumanavar have sung about the unlimited capabilities of the Siddhas. Siddhis emerge due to several causes.
It unfortunate that siddhis have always been considered more a hindrance to spiritual development than as yogic attainments. Saint Ramalingam, who has discussed the siddhis in detail, refers to the attainment of siddhis as pichu or childish play (pillai vilaiyattu). According to Pathnjali, siddhis are perfections in the waking state (vyutthana) but represent obstacles in the state of samadhi, and allows them no importance for the attainment of deliverance. Patanjali drew attention not only to the danger of exhibiting siddhis, but to the dangers that they present to the possessor; for the yogin is in danger of yielding to the temptation of magic, of being content to enjoy the siddhis instead of sticking to his spiritual talk of obtaining final liberation. Pattinattar calls siddhi as bitter sugarcane (kasakkum karumbu) to indicate its dual nature.