They were written between the year 50 and the year 140 of the Hegira.

When the history of the Jewish schools in the ages which immediately preceded and followed the birth of Christianity shall be written, no one will make any scruple of attributing to Hillel, Shammai, Gamaliel the maxims ascribed to them by the _Mishnah_ and the _Gemara_, although these great compilations were written many hundreds of years after the time of the doctors in question.
As to those who believe, on the contrary, that history should consist of a simple reproduction of the documents which have come down to us, I beg to observe that such a course is not allowable.

The four principal documents are in flagrant contradiction one with another.
Josephus rectifies them sometimes.

It is necessary to make a selection.

To assert that an event cannot take place in two ways at once, or in an impossible manner, is not to impose an _a priori_ philosophy upon history.