Evidently they can have no value beyond what is possessed by their common source; if they differ from it, it can only be in virtue of new errors; it would be waste of time to study their variations. Having eliminated these, we have before us none but independent copies, which have been made directly from the archetype, or secondary copies whose source (a copy taken directly from the archetype) has been lost. In order to group the secondary copies into families, each of which shall represent what is substantially the same tradition, we again have recourse to the comparison of errors. By this method we can generally draw up without too much trouble a complete genealogical table (stemma codicum) of the preserved copies, which will bring out very clearly their relative importance. This is not the place to discuss the difficult cases where, in consequence of too great a number of intermediaries having been lost, or from ancient copyists having arbitrarily blended the texts of different traditions, the operation becomes extremely laborious or impracticable. Besides, in these extreme cases there is no new method involved: the comparison of corresponding passages is a powerful instrument, but it is the only one which criticism has at its disposal for this task.
When the genealogical tree of the manuscripts has been drawn up, we endeavour to restore the text of the archetype by comparing the different traditions. If these agree and give a satisfactory text, there is no difficulty. If they differ, we decide between them. If they accidentally agree in giving a defective text, we have recourse to conjectural emendation, as if there were only one copy.
It is, theoretically, much more advantageous to have several