Lastly, there is the incontrovertible fact that Amidis de Gaula exists in Castilian, while it remains to be proved that it ever existed in Portuguese.
It by no means follows, however, from this incontrovertible evidence that the acquisition either of the jaw or of the lateral fins had not been in itself an extremely gradual process.
It is often stated, as if it were incontrovertible, that conscription and large standing armies are a menace to peace, and yet, although throughout the civilized world, except in the British Empire and the United States, conscription is the system employed for the recruiting of the national forces of both defence and offence, few of these countries show any particular disposition to make war.
At any rate, the incontrovertible facts of the Vinland voyages are that Leif and Thorfinn were historical characters, that they visited, in the early part of the 11th century, some part of the American continent south-west of Greenland, that they found natives whose hostility prevented the founding of a permanent settlement, and that the sagas telling of these things are, on the whole, trustworthy descriptions of actual experience.
The duration of the reigns in several dynasties is fairly well known from the incontrovertible evidence of contemporary monuments.