The perspectives of Heraclitus and Parmenides are almost diametrically opposed. Plato attempted to combine them both and produced the "first great rational system," which was significantly different from both. However, the term "rational" was not employed in the same sense it is now. Plato coined the term "Forms" to describe a "ideal standard" that characterizes reality... without regard to our sensory perceptions.
“There is only change,” Heraclitus said, “constant, relentless, and without end... “You can't step into the same river twice... "The Father of Relativism," he says, "a relativism on the verge of embracing chaos."
“The one principle Heraclitus did adopt was that of the Logos, which can be interpreted as the Word, Spirit, Reason, or even the Way—indeed, the parallels between Heraclitus' Logos and the Chinese Tao are striking.”
“In response to Heraclitus' assertion that everything changes, Parmenides replied by claiming that nothing changes.”
“Everything that exists—air, fire, and everything else—forms a single perfect whole,” he said.
“...two opposing perspectives on reality and the world. Yet it was Socrates and Plato's tremendous achievement to bring these two perspectives together and give birth to history's first major rational system.”
“Plato's Socrates never goes into detail about the relationships between God and the soul, the afterlife, and the Forms—and never explains how these Forms create the material reality of appearances in this world.”
“Plato shows that the ideal Forms, the models of perfection from which God created the visible world, are simply numbers.”
“What makes our puppy real, according to Plato, is his participation in the ideal Form of Puppiness... all the dogs and puppies we see are only copies of an ideal standard that defines what and who they are.”
Above are quotes from The Cave and Light
From The Passion of the Western mind: Understanding the ideas that have shaped our World view. By: Richard Tarnas
“It is critical to the platonic idea that these forms are primary, and that the visible objects of conventional reality are direct descendants of these forms. Platonic forms are not abstract concepts created by the human intellect by generalizing from a set of particulars. Rather, they have a character of existence, a level of reality, that surpasses that of the physical world.
Platonic archetypes both create and exist outside of the world. They appear and disappear throughout time, yet they are timeless. They are the obfuscated essence of things.”
“... A particular thing is what it is as a result of the ideas that went into its creation.”