The work of Parmenides of Elea set the scene for Greek philosophy to come and the concept of nous was central to his radical proposals. He claimed that reality as the senses perceive it is not a world of truth at all, because sense perception is so unreliable, and what is perceived is so uncertain and changeable. Instead he argued for a dualism wherein nous and related words (the verb for thinking which describes its mental perceiving activity, noein, and the unchanging and eternal objects of this perception noēta) describe a form of perception which is not physical, but intellectual only, distinct from sense perception and the objects of sense perception.