What historical research methods did Leopold von Ranke establish in Zur Kritik neuerer Geschichtsschreiber?

In his work Zur Kritik neuerer Geschichtsschreiber ("Critique of Modern Historians"), Leopold von Ranke established critical methods that became foundational to modern historical scholarship.1

He argued that the historian's primary task is the critical analysis of tradition and the objective reconstruction of the past, famously stating that history should show how it "actually was" (wie es eigentlich gewesen). To achieve this, he emphasized the following research methods:12

• Prioritizing Primary Sources: Ranke insisted on the acquisition of first-hand information and a tireless search for relevant data.1
• Defining Source Material: He identified essential evidence as memoirs, diaries, letters, reports from embassies, and original narratives from eyewitnesses.1
• Critical Evaluation: He demonstrated the necessity of scrutinizing sources for reliability, using the historian Guicciardini as an example of faulty practice; he showed that Guicciardini invented speeches and relied on secondary accounts rather than personal knowledge.1

Through these methods, Ranke shifted historiography toward a rigorous, evidence-based discipline, later reinforced by his "laboratory" seminars where students learned to seek out and critically produce documents.1