Unlike the natural philosophers preced him Plato describes the world cognitively. He proposes  Plato's ideas are still the bedrock of psychology today. 

When we think psychology our mind usually gravitates to people like Freud or Yung, but all modern ideas can be traced back to Plato. He was among the first to discuss the soul, about God as a abstraction of perfect form etc ....

We have all sorts of divisions we operate with:

• short term interests (governed by pain& pleasure) vs our long term desires
• subconscious vs the conscious mind,
• reptilian vs the mammal brain
• etc...

All of these started with Plato. He looked into diferent ways of knowing, and looked into which states of mind are more reliable than others. He divided the world into:

• the intelligible, best understood through reason
• the visible, best understood through our senses

Our senses are not good enough to understand true reality. What we may take as reality might as well be just shadows of the real thing.