And exactly the same is true of the Old Testament. There is no independent evidence whatsoever for your preposterous assertion that Judaism was founded by a god speaking on the top of a mountain - you just believe in a book because you believe in it, which is circular reasoning.
I was responding to someone who already believes in the authority of the Hebrew Bible. My argument was based on "if, then." IF, as my opponent believes, the "old testament" is from G-d, does it then authorize the "new?" I assert that it does not. I regard chr*stians who declaim against the qur'an, the Book of Mormon, etc., on the grounds that "if it's new it ain't true" while waving their "new testaments" in the air as hypocrites. What is the difference between the "new testament" and all these other "successors" to the Hebrew Bible other than the amount of time they have been around? None.
My argument was thus not aimed at someone who rejects the authority of the TaNa"KH. For my dialogue partner and myself belief in the authority of the TaNa"KH is the "antecedent." This being the case neither of us can deny it in debate ("denial of the antecedent" being a fallacy just as is "affirmation of the consequent").
As for someone who does not accept the TaNa"KH (such as yourself), your claim that belief in it is completely groundless is not as good as you might think. Unfortunately, most non-Jews know so little about the Torah (even though they flatter themselves that they do) that they know next to nothing about the safeguards built into it precisely to provide assurance that it is indeed from Heaven. These include complex codes at equidistant letter spaces which could not have been the creation of a human author (the key word here being "complex," as "beyond the range of mere coincidence") as well as the system of laws governing the writing of a kosher Torah Scroll. These laws include the requirement that each new scroll be copied from an already completed Torah Scroll. Why would this be so if, as you and your "rationalist" comrades assert, the Torah is a splice of various oral traditions dating back to the Second Temple era? The whole idea is that there was always an already complete Torah Scroll from which to copy a new one, going all the way back to the first scroll written by Moses at HaShem's dictation.
Furthermore, the Torah constantly insists it can be corroborated by simply asking one's parents. In other words, one's parents received their knowledge of the Torah from their parents, and so on down the generations from the Revelation at Sinai. If there was no such Revelation this was surely a foolish claim to make. Why would the Torah, if it were not given at Sinai, encourage the doubter to ask his own parents what they themselves had received? Eventually one would come to a generation to which these things had been artificially introduced and the claim of Sinaitic antiquity would be refuted. In fact, as the website of 'Aish HaTorah points out (see thispage for an overview), the very nature of a public and national revelation (as opposed to a private one communicated to a single individual) is that it can never be denied or counterfeited. It is rooted in the national memory going back to the event itself and this serves as an assurance that it is not a fraud introduced at a later date. And on top of all this, the Torah actually goes out on a limb to claim that this sort of national revelation will never happen again. Why would a man-made religion go out on a limb like this when it could so easily be disproven by a similar revelation?
I am afraid that your "18th Century" skepticism is nothing more than a charming museum piece, a relic of an earlier and extremely naive age. Perhaps you should actually learn a little about the Torah (from the people who actually know what they're talking about) before you make such broad assumptions and claims based on my argument with someone whose beliefs rest on a different set of assumptions than yours.
One of which are the traditions which have been handed down over the millenia to remember such as "Passover" which relates the story in a specific way to support its rememberance.
Also, there are later writings in Hebrew which talk of the same events which were written closer to the time of the events supposed occurance. These writings are called the "Mishna", a terse collective of law that explained basic meanings of the "OT" only hundreds of years after the supposed date of the writing of the 5 books. Just because a history is old, does not necessarily make it false (or true). There is a great deal of written material from these times. Combined with traditions and events, it becomes a great deal less easy to deny events that were described. It is indeed a question, but not necessarily one with a defintive conclusive answer.