Parmenides, answered from the texts and cited to the page.
The question is not quite right in its framing, and the framing matters. What I refused was not change as a brute fact of mortal experience — I refused it as a characterization of what genuinely is. The distinction is everything. The argument runs from the route itself. Whatever genuinely is cannot have come to be, for if it came to be it would have come from Not-being — and Not-being affords Being no birthplace, nothing no parentage.1
The image is deliberate: as the epic hero names his city and his father, so Being would need a source and a moving cause if it were to have been generated. Not-being supplies neither.2 What could have prompted it to come into being at one moment rather than another? Nothing beside Being exists to serve as that moving cause, and without a moving cause, generation is not merely absent but inconceivable.3
The same reasoning closes off perishing. Since there can be nothing beside Being — παρὰ τὸ ἐόν, alongside what-is — no efficient cause exists to unmake it either.4 Justice, which I name here as the figure of logical necessity, has not unchained Being and moved it to come into being or to perish.5 The fetters hold in both directions. Now, what follows from this is not the absurdity that nothing happens in the mortal world.
What follows is that whatever genuinely is — whatever satisfies the semata of B8, the signs deduced along the route of is — cannot be characterized by generation or destruction. The physical world that mortals inhabit, and that my own cosmology in the Doxa describes, is the realm where being and not-being are mixed in the way the route of is refuses.
Melissus read my non-temporal being temporally, as if I were saying Being always was and always will be; that is not what I meant.6 I meant that Being is all together now, outside the temporal sequence entirely — a non-temporal completeness, not an everlasting duration. The Peripatetic formula captures the consequence precisely: what is other than what-is is not.7
The physical world, the realm beside Being, is characterized as devoid of Being in the strict sense. That is not a denial that the world is there. It is a denial that the world, as mortal cognition apprehends it — mixed, changing, generated, perishable — can be the object of the genuine knowing the route of is delivers.
Not-being affords Being no birthplace and Nothing no parentage. The expressions γένναν ('parentage') and αὐξηθέν ('grown') must be given their full value; P.'s notion of origin and development derives directly from the birth and growth of living creatures.The Fragments of Parmenides, pp. 317–318
The two following arguments also, which deal successively with the source (ll.7-9) and the moving cause (ll.9-10) of Being, are analogous to the standard epic response, e.g. ἐξ Ἰθάκης γένος εἰμί, πατὴρ δέ μοί ἐστιν Ὀδυσσεύς ['I am from Ithaca by birth and my father is Odysseus'].The Fragments of Parmenides, pp. 317–318
The locution 'certainty will never be strong enough to impel...' expresses the same thought as 'what occasion could have prompted...?' (l.9) and is itself paraphrased by 'justice has not moved...' (l.14); all exclude from Being the operation of efficient causation.The Fragments of Parmenides, pp. 319–320
Since there can be nothing 'beside Being' (ll.12-13) and therefore no moving cause, Being is imperishable as well as ungenerated.The Fragments of Parmenides, pp. 320–321
P. concludes that 'justice did not unchain Being and move it either to come into being or to perish.' The verb ἀνιέναι ['loosen'] (l.14) when followed by the infinitive is close in sense to ἐφιέναι ['let'] (12) but less positive... it continues the allusion to a moving cause in ὦρσεν ['urged'] (l.9) and ἐφήσει ['let'] (l.12) and signifies that perishing, as well as coming to be, is inconceivable without it.The Fragments of Parmenides, pp. 320–321
the expression was interpreted temporally by Melissus ('since it did not come to be but is, it always was and always will be and has no beginning or end' etc., fr. 2) but is meant by P. to denote a non-temporal being ('it never was nor will be, for it is all together now', l.5).The Fragments of Parmenides, pp. 319–320
The argument was developed correctly in the Peripatetic formula τὸ παρὰ τὸ ὂν οὐκ ὄν ['what is other than what-is is not'] (tt. 26, 36, 42), which Alexander, Syrianus and Asclepius rightly referred to the physical world (tt. 208, 162, 191), thus characterised as devoid of Being.The Fragments of Parmenides, pp. 320–321