of cd to ef, so that we have to decide whether the true reading of β is found in cd or in ef. The final clear result is that, when we have gone as far as the discoverable relations among our documents admit, we have on the one hand banished a considerable number of the extant variants as absolutely excluded, and on the other ascertained a considerable number of readings of O, in addition to those parts of the text of Ο in which all its descendants agree.
71. Two elements of uncertainty as to the text of Ο alone remain. First, the condition presupposed above, absence of mixture from without, does not always hold good. Where mixture from without exists, the inference given above from the concurrence of γ with δε against αβ becomes but one of three alternatives. It is possible that mixture with a text independent of Ο has affected γ and Υ alike, but not αβ; and if so, αβ will be the true representatives of X and of O. This possibility is however too slight to be weighed seriously, unless the reading of γ and Υ is found actually among existing documents independent of O, provided that they are fairly numerous and various in their texts, or unless the hypothesis of mixture is confirmed by a sufficiency of similarly attested readings which cannot be naturally derived from readings found among the descendants of O. Again, it is possible that the reading of αβ is itself due to mixture with a text independent of Ο: and if so, though rightly rejected from the determination of the reading of O, it may possibly be of use in determining the reading of an ancestor of O, or even of the autograph itself. But both these contingencies need be taken into account only when there is already ground for supposing mixture from without to exist.
72. The second element of uncertainty is that which always accompanies the earliest known divergence from a single original. Given only the readings of X and Y, Genealogy is by its very nature powerless to shew which were the readings of O. It regains its power only when we go on to take into account fresh documentary evidence independent of O, and work towards an older common original from which both it and Ο are descended. Ο then comes to occupy the place of X or Y, and the same process is repeated; and so on as often as the evidence will allow. It must however be reiterated (see § 52) that, when Ο has come to mean the autograph, we have, in reaching the earliest known divergence, arrived