The significance of such figures in human progress has been debated. Some think they play a crucial role, while others say they have little impact on the broad currents of thought and social change. The concept is generally used in the sense that the person really existed in the past, as opposed to being legendary. However, the legends that can grow up around historical figures may be hard to distinguish from fact. Sources are often incomplete and may be inaccurate, particularly those from early periods of history. Without a body of personal documents, the more subtle aspects of personality of a historical figure can only be deduced. With historical figures who were also religious figures attempts to separate fact from belief may be controversial.