Plato favored a doctrine relating to the immortality of the "soul" and he developed an idea called "the theory of Forms." Taking the form of written dialogues, he presented accounts relating to unreality/reality, knowledge,the nature of humanity and God, society, and beauty. Poetry was regarded with suspicion, perhaps because it tended to "poetify" certain circumstances in a way that would lead to illusion and influence impressionable suggestible people - such as the young. Although a poet himself, he saw many other poets as being anti-philosophical. Philosophy is analytical and history is factual - combining the two in an emotive poem he saw to be rather risky. Poetry is of course mostly beautiful and many people see that as being the whole point of it - it also speaks to the heart and the emotions which can often lead us into unreality where we aspire and dream. Perhaps Plato saw those dreams as mere illusions of unreality - heights that could never be reached in the real world.