If Heraclitus is the early champion of change, the partisan of permanence is another early Greek philosopher, Parmenides, who asserted that there is no change, period.
His position contra change can be stated as follows: Being is and Being is One; change and plurality are both illusions. If anything becomes, it either comes to be out of being or non-being. But if out of being, then it already is; there is no real coming to be. And from non-being, or nothing, only nothing can come. Becoming, therefore, is an illusion.
Now, since becoming, or change, is clearly apparent in the everyday world of ordinary sense perception, Parmenides is not talking about appearances but about a truth known to reason which can see beyond appearances. This is a first approximation of a distinction that Plato would later make, with more generality, between knowledge and opinion, thought and sense. It is an important distinction, philosophically, since it forms the basis of all varieties of idealism.
Because of this distinction and his assertion that Being is unchanging, uncreated, and complete just as it is, Parmenides has been called the father of idealism. Indeed, these are central tenets of idealism but, as Frederick Copleston1 convincingly argues, Parmenides used them to establish not idealism but a monistic materialism.
Although the One of Parmenides can be grasped only in thought, there is, as Copleston points out, a big difference between “being grasped in thought” and “being thought.”
Note
1. Frederick Copleston, A History of Philosophy: Greece & Rome (Volume 1). His discussion of Parmenides is on pages 64-70.
HyC