Yesterday, I told about Angelo Poliziano, the man who realized that ancient sources are sometimes dependent on each other and should be dealt with accordingly: the original source can be used, the secondary text can be eliminated. Poliziano applied this principle also on the medieval manuscripts that had so diligently been copied by countless anonymous monks: realizing that manuscripts could depend on earlier manuscripts, he proposed the elimination of secondary manuscripts. This was the beginning of what is called textual criticism, the study of texts in order to reconstruct their original wording.
Our Greek, Latin, and Hebrew sources are handed down to us in medieval manuscripts, and because it is humanely impossible that a scribe copies a long text without mistakes, our manuscripts contain scribal errors. In the Middle Ages, copiists had often recognized these mistakes and had tacitly corrected them. However, their conjectures were usually pure guesswork. In fact, the medieval scribes contributed to the proliferation of errors.