Parmenides:

Of the presocratic philosophers Parmenides might be among the most influential and yet divisively interpeted. We only know of one work by him, a poem of which only the introduction has survived in its entirety. Despite the sparse material there are many different interpretations of Parmenides, each and every word is weighed carefully and testimonies analyzed.

The poem starts with Parmenides being taken by godesses to a realm between night and day. As a man of knowledge he is above mortals and is taken to his hearts desire. The godesses tell him that he will learn two ways of seeking, the way of truth and the way of foolish mortals. The path of trust is the way that things are and cannot not be, attended by truth. The path of mortals is the way that it is not and it cannot be. This path is forbidden as it is unending, If A is, then not A is infinite. What is unbounded must be forbidden.

The way of trust posits that thinking and being can be the same. Not literally as something will physically exist if you think of it, but in an ontological and epistemological sense. You can think of something, reason about it, as it is and identify the limits that bind it. A square for example can be reasoned about the distance between its corners. There is nothing beyond the corners and we are only concerned about what is contained inside the limits.

There are further consequences of thinking. When we think of something, it must be, for we cannot think of something that is not. What we are thinking of exists before and after our thoughts. Parmenides asserts that for something to be it must always have been. Since there is no such thing as nothing it is impossible for things to start existing from nothing, and even then it would be absurd as there is nothing to influence when nothing would give birth to something. Parmenides also asserts that the thing that is must be indivisible, homogenously distributed and entirely unchanging. For if something is divisible it is not one thing, but multiple.

There is a division of interpretation whether the ontology of Parmenides is restricted to a singular one or if there can be multiples of it.

We know barely anything about the path of appearance as there is no substantial surviving fragments and what ancient accounts have survived put little attention to it. We know involves dualism of light and dark and warmth and cold from testimonies, but nothing substantial. It is confusing as to why this elemental system would be introduced after change and multiplicity has seemingly been eliminated logically. It is thought that these two separate systems respectively explain the static world of reason and the changing world of the senses. The later is imperfect and is not the real truth, but its the best possible explanation for the senses that Parmenides gives us. Testimonies from antique philosophers with access to Parmenides works seems to support that they at least did not see a puzzling conflict with Parmendides philosophy.

Notes:

Understanding being and why something that exists must always have been reminds me of an event in a fantasy setting that confuses many. In Warhammer 40k there is an immaterial dimension called the warp which is the realm of emotion and concept. After a catastrophic event Slaanesh, a chaos god of desire, is born. And since it exists in the realm of ideas, it must always have been and cannot cease to be. Thus this god influences events in time before its own birth. This is very puzzling for the fans of the series, but with Parmenides understanding of being one can explain it.

Both nothingness and infinity are banished by Parmenides. The infinity of negation and nothingess appear similar in their lack of bounds.