Parmenides means that all men — common men and philosophers alike — are agreed to believe in the reality of the world our senses seem to show us. The premiss they start from is neither the recognition of the One Being only (from which follows the Way of Truth and nothing more) nor the recognition of an original state of sheer nothingness (which would lead to the impassable Way of Not-being). What mortals do in fact accept as real and ultimate is a world of diversity, in which things "both are and are not", passing from non-existence to existence and back again in becoming and perishing, and from being this ("the same") to being something else ("not the same") in change. The elements, they think, are modified or transformed on a "way to and fro", that turns back upon itself". Becoming, change, and the diversity they presuppose must be assumed in any cosmogony. They will be assumed in the cosmogony of the second part. But Parmenides alone perceives that at this point error begins to go beyond the limits of truth.