Like Xenophanes, Parmenides developed his philosophical convictions in a didactic poem, composed in hexameter verse, entitled (Plnt. de Pyth. Orac. p. 402), the poetical power and form of which even his admirers do not rate very highly (Proclus, in Parmen. 4.62; Plut. de Audit. p. 44, de audiend. Poet. p. 16c.; comp. Cic. Acad. Quaest. 4.23); and this judgment is confirmed by the tolerably copious fragments of it which are extant, for the preservation of which we are indebted chiefly to Sextus Empiricus and Simplicius, and the authenticity of which is established beyond all doubt by the entire accordance of their contents with the statements in Aristotle, Plato, and others, as well as by the language and style (the expressions of Diogenes Laert. 9.23, have reference to Pythagoras, not to Parmenides). Even the allegorical exordium is entirely wanting in the charm of inventive poetry, while the versification is all that distinguishes the argumentation from the baldest prose. That Parmenides also wrote in prose (Suid. s. v.) has probably been inferred only from a misunderstood passage in Plato (Soph. p. 237). In fact there was but one piece written by Parmenides (D. L. 1.16, comp. Plat. Parmen. p. 128a. c.; Theophrastus in D. L. 8.55; Simplicius on Arist. Phys. f. 31, a. and others); and the prose passage, which is found among the fragments (Sinplic. l.c. f. 7), is without doubt of later origin, added by way of explanation (comp, Simon Karsten, l.e. p. 130).

In the allegorical introduction to his didactic poem, the Eleatic describes how Heliadic virgins conducted him on the road from Darkness to Light, to gates where the paths of Night and Day separate ; and, after Dike had unbolted the gates, to the goddess Wisdom. She greets him kindly, with the promise of announcing to him not only the unchangeable heart of truth (ἀληθείης εὐπειθέος ἀτρεκὲς ἦτορ), but also the truthless fancy of men (Parmenid. Reliqu. in Simon Karsten, l.c. 32, after Sextus Empiricus, ad v. Math. 7.111), and indicates in this way whither each of these opposite roads leads, while she at the same time points to the division of the poem into two parts. The path of truth sets out from the assumption that existence is, and that non-existence is inconceivable (Reliqu. 50.33. &c.), but only leads to the desired end by the avoidance, not merely of assuming a non-existence, but also of regarding existence and non-existence as on a par with each other, which is the back-leading road of the blind and erring crowd (ib. 1. 43, &c.). On the former, Reason (λόγος, νοῦς) is our guide; on the latter the eye that does not catch the object (ἄσκοπον ὄμμα), and re-echoing hearing (ἠχήεσσα ακουή, ib. 1. 52. &c. comp. 1. 89; Plat. Parmen. p. 135d.). On the former path we convince ourselves that the existent neither has come into being, nor is perishable, and is entirely of one sort (οὖλον μουνογενέσυνογενές), without change and limit (καὶ ἀτρεμὲς ἠδʼ ἀτέλεστον), neither past nor future, entirely included in the present (ib. 1. 56). For it is as impossible that it can become and grow out of the existent, as that it could do so out of the non-existent; since the latter, non-existence, is absolutely inconceivable, and the former cannot precede itself; and every coming into existence presupposes a non-existence (1. 61, &c.). By similar arguments divisibility (1. 77, &c.), motion or change, as also infinity, are shut out from the absolutely existent (1. 81, &c.), and the latter is represented as shut up in itself, so that it may be compared to a well-rounded ball (1. 100, &c. ); while Thought is appropriated to it as its only positive definition, Thought and that which is thought of (Object) coinciding (1. 93, &c.; the corresponding passages of Plato, Aristotle, Theophrastus, and others, which authenticate this view of his theory, see in Commentatt. Elcat. by the author of this article, i. p. 133, &c., and in S. Karsten, l.c.). Thus to Parmenides the idea of Being had presented itself in its complete purity, to the exclusion of all connection with space, time, and multiformlity, and he was compelled to decide upon regarding as human fancy and illusion what appears to us connected with time and space, changeable and multiform (1. 97, &100.176), though he nevertheless felt himself obliged at least to attempt an explanation of this illusion. In this attempt, which he designates as mere mortal opinion and deceptive putting together of words, he lays down two primordial forms (μορφαὶ), the fine, and light, and thoroughly uniform aetherial fire of flame (φλογος αἰθέριον πῦρ), and the cold, thick, and heavy body (δεμας) of dark night (1. 112, &c.),--represented by those who have preserved to us the in formation, as Warm and Cold, Fire and Earth (Arist. Phys. 1.3, Metaph. 1.5, de Gener. et Corrupt. 1.3; Theophrast. in Alex. l.c.); the former referred to the existent, the latter to the non-existent (Arist. and Theophr. ll. cc.). Although the latter expressions are not found in Parmenides, he manifestly regarded the former, the primordial principle of fire, as the active and real, the other as the passive, in itself unreal, only attaining to reality when animated by the former (1. 113, 129). The whole universe is filled with light and darkness (1. 123), and out of their intermingling every thing in the world is formed by the Deity, who reigns in their midst (1. 127. ὲν δὲ μέσῳ τούτων δαίμων ἡ πάντα κυβερνᾷ), the primary source of the fateful procreation and intermingling (στυγεροῖο τοκον καὶ υίξιος ἀρχὴ, 1. 127, &c.). As the first of the gods, this deity devised Eros, the principle of union between the mutually opposed primordial principles (Arist. Metaph. 1.4; Sext. Empir. ad v. Math. 9.1, 6; Plut. de Primo Frigido, p. 946e.); and after him other gods, doubtless to represent powers and gradations of nature (Plato, Symp. p. 195c.; Menand. de Encom. 1.100.5), amongst which Desire, War, and Strife may very well have been found (Cic. de Nat. Deor. 1.11; S. Karsten's Conjecture, l.c. p. 239, does not seem requisite). But the ultimate explanatory principle of the world of originated existence must, in his view, have been necessity, or destiny, and as such he may very well have designated at one time that deity that holds sway between the opposites (Stobaeus, Eclog. 1.23, p. 482; comp. Plato, Symp. p. 195c.), at other times the opposed principles themselves (Plut. de Anim. Proereat. c. Timaeo, p. 1026b.). Of the cosmogony of Parmenides, which was carried out very much in detail, we possess only a few fragments and notices, which are difficult to understand (1. 132, &c.; Stob. Ed. Phys. 1.23, p. 482, &c.; Cic. de Nat. Deor. 1.11, &c.; comp. S. Karsten, l.c. p. 240, &c.), according to which, with an approach to the doctrines of the Pythagoreans, he conceived the spherical mundane system, surrounded by a circle of the pure light (Olympus, Uranus); in the centre of this mundane system the solid earth, and between the two the circle of the milky-way, of the morning or evening star, of the sun, the planets, and the moon; which circle he regarded as a mixture of the two primordial elements. As here, so in his anthropological attempts, he deduced the differences in point of perfection of organisation, from the different proportions in which the primordial principles were intermingled (S. Karsten, p. 257, &c.), and again deduced the differences in the mental capacities from the more or less perfect intermixture of the members (ὡς γαρ ἑκάστῳ ἕχει κρᾶσις μελέων πολυπλάγκτων, τὼς νόος ἀνθρώποισι,, 1. 145, &c.; comp. S. Karsten, p. 266, &c.) ;--laying down in the first instance that the primordial principles are animated, and that all things, even those that have died, partake of feeling, not indeed for the warm, for light, for sound, but for the cold, for darkness, and for silence (Theophrastus, de Sensu Princ.). Accordingly, consciousness and thought also, in so far as, while conceived in a state of change, it is an object of appearance, is to be deduced from the primordial principles of the world of phaenomena, but must be abstracted from that Thought which is coincident with the absolutely existent. But, however marked the manner in which Parmenides separated the true, only, changeless Existence from the world of phaenomena, which passes off in the change of forms, and however little he may have endeavoured to trace back the latter to the former, the possibility of its being so traced back he could not give up, and appears for that very reason to have designated the primordial form of the Warm as that which was real in the world of phaenomena, probably not without reference to Heracleitus' doctrine of perpetual coining into existence, while he placed along with it the opposite primordial form of the Rigid, because it was only in this way that he could imagine it possible to arrive at coming into existence, and change. Thus, however, we find in him the germs of that dualism, by the more complete carrying out of which the later Ionians, Empedocles, Anaxagoras, and others, imagined that they could meet the Eleatic doctrine of the absolute. Empedocles seems more immediately, and to a greater extent than the rest, to have further developed these germs; and he also, just like Parmenides, set down necessity or predestination as the ultimate ground of originated existence and change, and in like manner agreed with his Eleatic predecessor in this. that like is recognised by like; a presupposition in which, as it occurs in Parmenides, we can scarcely fail to recognise a reference to his conviction that Thought and Existence coincide. But, little as he could deny that the really existent must in some way or other lie at the basis of change and the multiformity of phaenomena, he could not attempt to deduce the latter from the former so long as he maintained the idea of the existent as single, indivisible, and unchangeable; and this idea, again, he could not but maintain, so long as he conceived it in a purely abstract manner as pure Position. * It may be necessary to suggest to the reader who is unaccustomed to the terminology of metaphysics, that in connection with this word Position he must dismiss all notion of locality, and look upon it as a noun whose meaning answers to that of the adjective positive.--TRANSLATOR. But, however insufficient this idea is, it was necessary to develope it with sharpness and precision before it would be possible to make any successful attempts to find the absolutely existent in place of the originated, and therefore as something multiform. The first endeavours to define the idea of the existent are found in Xenophanes, and with them begins that course of development peculiar to the Eleatics. But Parmenides was the first who succeeded in developing the idea of the existent purely by itself and out of itself, without carrying it back and making it rest upon a support, like the Deity in Xenophanes. It is only from inaccurate or indistinct statements that it has been concluded that Parmenides represented the absolutely existent as a deity (Ammonius, in Arist. de Interpret. f. 58; Arist. de Xenoph. Gonry et Melisso, 100.4). So that he was the only philosopher who with distinctness and precision recognised that the existent, as such, is unconnected with all separation or juxtaposition, as well as with all succession, all relation to space or time, all coming into existence, and all change; from which arose the problem of all subsequent metaphysics, to reconcile the mutually opposed ideas of Existence and Coming into Existence.