Upvote:1
Of course we cannot be sure. Even for relatively public recent events, with TV reporters recording whatever the camera was pointed at and access to government records, we can't know what wasn't recorded or if the people who wrote the records misrepresented the truth.
What you call "theoretical" might be better described as "taking a critical look at sources." The historian looks at as many records as feasible and asks the questions:
A bit like a judge and jury looking at a criminal case. And just as in the justice system, every now and then the historians get it wrong. Sceptics or minority opinions might have been right for all the right reasons, or because even a stopped clock shows the right time twice a day.
Upvote:6
To address the question about Egyptian Hieroglyphics, we can be sure that our readings are mostly correct. The initial key to reading them was the Rosetta Stone, which had the same text in three different languages:
Figuring out ancient Egyptian was not simple, because the script works rather differently from most written languages, but it was gradually achieved. It was already known that the spoken Egyptian language was an ancestor of Coptic, which is still used by the Coptic Church in Egypt. That gave significant clues to pronunciation and grammar. As understanding developed, it became possible to trace changes in the language and its writing through the history of Egypt, and those changes were reasonably in accord with what we know from other regions of the world about the way languages change over time.
There are a great many surviving samples of Egyptian, on papyri, in tombs, and lots of inscriptions on statues and temples. And they all make sense. At this point, it becomes completely implausible that we're misinterpreting the script in any fundamental way, because there are just too many texts that make sense. There were spurious claims of translation before the script was understood, but they fell apart when applied to a text that the author didn't study.
Further, the ability to read Egyptian was important in deciphering Old Persian Cuneiform, and our readings of that language are internally consistent, making the idea that we have Egyptian wrong even less plausible.
Finally, new bilingual texts are occasionally discovered. The readings of the Egyptian text, which we've never seen before, are in accordance with the other language(s) of the text.