case they are all fragments, usually casual and scattered fragments, of a genealogical tree of transmission, sometimes of vast extent and intricacy. The more exactly we are able to trace the chief ramifications of the tree, and to determine the places of the several documents among the branches, the more secure will be the foundations laid for a criticism capable of distinguishing the original text from its successive corruptions. It may be laid down then emphatically, as a second principle, that all trustworthy restoration of corrupted texts is founded on the study of their history, that is, of the relations of descent or affinity which connect the several documents. The principle here laid down has long been acted upon in all the more important restorations of classical texts: but it is still too imperfectly understood to need no explanation. A simple instance will show at once its practical bearing.
50. Let it be supposed that a treatise exists in ten MSS. If they are used without reference to genealogy by an editor having a general preference for documentary evidence, a reading found in nine of them will in most eases be taken before a rival reading found only in the tenth, which will naturally be regarded as a casual aberration. If the editor decides otherwise, he does so in reliance on his own judgement either as to the high probability of the reading or as to the high excellence of the MS. He may be right in either case, and in the latter case he is more likely to be right than not: but where an overwhelming preponderance of the only kind of documentary evidence recognised is so boldly disregarded, a wide door is opened for dangerous uncertainty.
51. Another editor begins by studying the relations of the MSS, and finds sufficient evidence, external or
