Early history of Shaivism is difficult to determine. However, the Śvetāśvatara Upanishad (400 – 200 BCE) is considered to be the earliest textual exposition of a systematic philosophy of Shaivism. Shaivism is represented by various philosophical schools, including non-dualist (abheda), dualist (bheda), and non-dualist-with-dualist (bhedābheda) perspectives. Vidyaranya in his works mentions three major schools of Shaiva thought— Pashupata Shaivism, Shaiva Siddhanta and Pratyabhijña (Kashmir Shaivism).
The forms of thought of this thing that is difficult to determine are?
Pashupata Shaivism, Shaiva Siddhanta and Pratyabhijña