Why did Leopold von Ranke emphasize using firsthand historical sources?

Leopold von Ranke emphasized the use of firsthand historical sources—such as memoirs, diaries, letters, embassy reports, and eyewitness narratives—to establish a rigorous, critical method of historical scholarship.1

His commitment to these primary materials was driven by his goal to show history "as it actually was" (wie es eigentlich gewesen), rather than using history to judge the past or provide moral lessons for the future. By prioritizing original documents, Ranke sought to avoid the faulty practices of earlier historians, such as the invention of speeches or the reliance on secondary accounts that lacked personal knowledge of events.1

This methodology transformed history into an academic discipline, as Ranke utilized his seminars as "laboratories" where students were trained to seek out and critically analyze documents. Ultimately, his focus on factual accuracy was rooted in his belief that history was a "holy hieroglyph," and that by meticulously uncovering the truth of the past, the historian could discern the divine plan manifest in the development of modern nation-states.1