Historians have long realized that, epistemologically speaking, the idea of learning what “really happened” through historical methodologies is fraught with difficulties that sometimes renders a solution essentially impossible, especially with ancient history. History is not an empirical discipline. We cannot directly observe the past. We can only indirectly observe the effects of the past. These effects generally consist of man-made materials that survive from the past: texts and artifacts (including art). Thus, historians cannot directly observe Moses. We can only directly observe what surviving ancient texts tell about Moses, or artifacts that may survive from Moses’ day (e.g. the Midianite tent-shrine and bronze serpent images found at Timna in the Negev, dating roughly to Moses’ time).
It is very important to note here that the existence of an ancient text that talks about Moses does not prove his historicity, nor does the lack of texts discussing Moses prove he did not exist. The reality of what did or did not exist in the ancient past is an ontological question that in many ways can never be resolved by historical methods. The question of how we, as twenty-first century historians can know about what did or did not exist in the past is an epistemological question. Ancient texts tell us only what the ancient author believed or thought happened—or, just as often, what the ancient author wants his readers to believe happened. We often have ample evidence for ancient people who were completely fictitious, and also often have no evidence whatsoever for ancient realities.