Apart from Ontology, Parmenides reckons all as belonging to human opinions. These were derived from the observations of sense (which he especially excludes from Ontology) with the comparisons, inferences, hypothesis, &c., founded thereupon: the phenomena of Nature generally.[68] He does not attempt (as Plato and Aristotle do after him) to make Ontology serve as a principle or beginning for anything beyond itself,[69] or as a premiss from which the knowledge of nature is to be deduced. He treats the two--Ontology and Phenomenology, to employ an Hegelian word--as radically disparate, and incapable of any legitimate union. Ens was essentially one and enduring: Nature was essentially multiform, successive, ever changing and moving relative to the observer, and different to observers at different times and places. Parmenides approached the study of Nature from its own starting point, the same as had been adopted by the Ionic philosophers--the data of sense, or certain agencies selected among them, and vaguely applied to explain the rest. Here he felt that he relinquished the full conviction, inseparable from his intellectual consciousness, with which he announced his few absolute truths respecting Ens and Non-Ens, and that he entered upon a process of mingled observation and conjecture, where there was great room for diversity of views between man and man. [Footnote 68: Karsten observes that the Parmenidean region of opinion comprised not merely the data of sense, but also the comparisons, generalisations, and notions, derived from sense. "[Greek: Doxasto\n] et [Greek: noêto\n] vocantur duo genera inter se diversa, quorum alterum complectitur res externas et fluxas, _notionesque quæ ex his ducuntur_--alterum res æternas et à conspectu remotas," &c. (Parm. Fragm. p. 148-149).] [Footnote 69: Marbach (Lehrbuch der Gesch. der Philos., s. 71, not. 3) after pointing out the rude philosophical expression of the Parmenidean verses, has some just remarks upon the double aspect of philosophy as there proclaimed, and upon the recognition by Parmenides of that which he calls the "illegitimate" vein of enquiry along with the "legitimate." "Learn from me (says Parmenides) the opinions of mortals, brought to your ears in the deceitful arrangement of my words. This is not philosophy (Marbach says): it is Physics. We recognise in modern times two perfectly distinct ways of contemplating Nature: the philosophical and the physical. Of these two, the second dwells in plurality, the first in unity: the first teaches everything as infallible truth, the second as multiplicity of different opinions. We ought not to ask why Parmenides, while recognising the fallibility of this second road of enquiry, nevertheless undertook to march in it,--any more than we can ask, Why does not modern philosophy render physics superfluous?"