History is Textual

Was the Zohar written by Rabbi Shimon Bar Yochai in the Tannaitic Era? Were the laws and practices of the "Torah She B'al Peh" in existence before the Tannaitic Literature. Did Jews always believe in an afterlife and a resurrection of the dead? And was God always understood as the unknowable, incorporeal God of Maimonides?

These questions and similar ones about ideas and beliefs in the ancient past can only be measured "scientifically" and historically in one way. Through writing. We simply have no other comparable way of checking what people were actually saying hundreds or thousands of years ago except by reading what writing these people left behind.

Of course this leaves a huge gap in our knowledge of historical time periods when writing was not as widespread as today but again it's all we really have.

So let's address for fun one of our examples. Did Jews always believe in a (meaningful) afterlife? All we can really say for sure is that the ideas of reward and punishment in Heaven and Hell only appear unambiguously in Jewish writings at a relatively late stage of Jewish history. Does the absence of (explicit) mention in earlier texts completely rule out the possibility that Jews always believed in such an afterlife? Not necessarily and it is always possible that by some fluke or "conspiracy" nobody bothered to make a passing mention of certain fundamental concepts of Judaism that feature so frequently in later Talmudic literature. Anything is possible.

But if we are to be historians we have to deal with the written data available to us and the data, by omission, rules out the this assumption. Again our data may be faulty. We might have lost a crucial text here or there which would have painted us a completely different picture. Nevertheless history like other more exact sciences can only deal with "observable" data.

So if you wish to assert that the Zohar was around for hundreds of years (despite no reference to it before the 13th century) or that Jews always keep the 39 melachot of Shabbat (despite no mention of them in the Tanach) I can't prove you wrong. But on the other hand if you assert things like this you're not being a "historian" and if you write that Ancient Hebrews wore tefillin and shook lulavim you're not writing history - just pure speculation - which is, at best based, on faith. 

Have your faith. But don't call it history.