The philosophy of idealism posits that reality is fundamentally mental or immaterial. It suggests that the material world is shaped by our perceptions and ideas, emphasizing the importance of the mind in understanding existence. Idealists argue that what we perceive as the physical world is a reflection of our thoughts and consciousness. One of the key figures in idealism is George Berkeley, who famously stated, "To be is to be perceived." This means that objects only exist as long as they are observed. Idealism contrasts with materialism, which asserts that the material world is the primary reality, independent of our perceptions.