Plato believed that the body was a prison for the soul. Plato thought that our souls are eternal and perfect, but are trapped inside temporary and imperfect meat suits. Plato says, for example, that before we’re born, our souls had a perfect understanding of the pure concept of number 5. We didn’t understand it as a number or as a word or even as a set of five objects. Rather, our souls enjoyed direct contact with the pure idea of 5 that shapes everyone’s understanding of 5 in the world. So when we learn to count, Plato says we’re not actually learning about 5, our souls are remembering what we knew about 5 before we got stuck in a crappy body. The true nature of a thing, its essence, precedes or comes before its existence in the world. Ideas about things exist independently of our understanding of those things. To Plato, we didn’t invent 5; it always existed. We just rediscovered it.
Aristotle said that our understanding of the world comes through our experiences. For Aristotle, we understand the essence of things only after we have had enough time to learn about them. Our souls are shaped by our experiences, and we form an idea about a thing after we learn about its characteristics. So Aristotle says that we learn about 5 because we experience our fingers and a basketball team and 3+2 and 25/5 and all these things together become our understanding of the idea of 5. So existence precedes essence.
For Aristotle, we understand what things are only because we have experienced them with our bodies.
Remember, kids: Plato says essence precedes existence; Aristotle says existence precedes essence.