Animism is the earliest concept towards the religion forwarded by Tylor himself. It is a belief in the existence of spiritual beings. Spirits are the ethereal embodiment without real flesh and blood.
Although they are non-material, but real enough for those who believes in it. Primitive use different names to refer those spirits- ghost, goblin, genii, trolls, fairy, witch, demon, devil, angel and even god. A spirit does not obey the laws of nature and can transcend matter , time and space.
This makes the spirits wonderful and mysterious, and therefore, they have been regarded as supernatural.