The title of "Father of Idealism" is not definitively attributed to a single philosopher. However, Plato is widely recognized as a foundational figure in the development of Idealism.
Plato's theory of Forms, as presented in his dialogues, posits the existence of a realm of perfect, unchanging Forms that are the true objects of knowledge. These Forms, such as beauty, justice, and goodness, are the ultimate reality, while the physical world we perceive is merely a shadow or reflection of this ideal realm.
This emphasis on a realm of perfect and eternal ideas, as opposed to the physical world, became a cornerstone of Idealist philosophy. Many subsequent philosophers, including George Berkeley, Immanuel Kant, and Georg Wilhelm Friedrich Hegel, built upon Plato's ideas, further developing and refining Idealism.
While Plato is often considered the "Father of Idealism", it's important to note that his philosophy is complex and multifaceted. He also explored other themes, such as the nature of the soul, the role of reason, and the ideal state.
However, Plato's influence on the development of Idealism is undeniable, making him a key figure in the history of this philosophical tradition.