Genuine or fake?

Spyglass

How should we investigate the Vinland Map?

How can we prove that the Map was drawn in 1440? How can we prove that it wasn't?

Tests for authenticity

It is not straightforward to prove that something happened in the distant past. What might constitute tests for authenticity? A dated bill of sale? A photograph of a mapmaker drawing our map? Even these would not constitute definitive evidence. The bill and/or the photograph could always have been faked.

Such tests are consistent with the Map being genuine... but they do not prove it. To establish proof, we have to test for falsity.

Tests for falsity

Consider an example. I test the ink on the Map and show that it contains a modern chemical. Ink on old maps cannot contain modern chemicals. Ergo I have proved that the Map cannot be an old map. I have falsified the statement that the Map is an old Map. What if my test had not shown modern chemicals? I would have shown that the test was consistent with the Map being an old map. I would not have proved it.

To establish proof, I must test not for authenticity but for falsity - not for compliance but for non-compliance.
Statement: Old maps do not contain modern chemicals.
Test: "Old Map" does contain modern chemicals.
Conclusion: "Old Map" is not an old map.

Another example:
Statement: The parchment of the "Old Map" must be 600 years old.
Test (carbon dating) The parchment of the "Old Map" is 600 years old.
Conclusion: The test is consistent with the "Old Map" being 600 years old.

Note that this proves nothing. It is a statement of consistency. Old parchment does not ensure an old map. A modern forger could use old parchment... and obviously would.

Such tests are consistent with the Map being genuine... but they do not prove it. To establish proof, we must test for falsity.

Any object that we consider authentic can, in principle, be shown to be a fake, if new evidence proves it. Authenticity is, in fact, an "interim" state, lasting as long as tests for falsity fail. On the other hand, the more the tests for falsity fail, the more likely the object is to be authentic.