Tannaitic exegesis distinguishes principally between the actual deduction of a thesis from a Bible passage as a means of proving a point, and the use of such a passage as a mere mnemonic device – a distinction that was also made in a different form later in the Babylonian schools. The Babylonian Amoraim were the first to use the expression "Peshaṭ" ("simple" or face value method) to designate the primary sense, contrasting it with the "Drash," the Midrashic exegesis. These two terms were later on destined to become important features in the history of Jewish Bible exegesis. In Babylonia was formulated the important principle that the Midrashic exegesis could not annul the primary sense. This principle subsequently became the watchword of commonsense Bible exegesis. How little it was known or recognized may be seen from the admission of Kahana, a Babylonian amora of the fourth century, that while at 18 years of age he had already learned the whole Mishnah, he had only heard of that principle a great many years later (Shab 63a). Kahana's admission is characteristic of the centuries following the final redaction of the Talmud. The primary meaning is no longer considered, but it becomes more and more the fashion to interpret the text according to the meaning given to it in traditional literature. The ability and even the desire for original investigation of the text succumbed to the overwhelming authority of the Midrash. It was, therefore, providential that, just at the time when the Midrash was paramount, the close study of the text of the Bible, at least in one direction, was pursued with rare energy and perseverance by the Masorites, who set themselves to preserving and transmitting the pronunciation and correct reading of the text. By introducing punctuation (vowel-points and accents) into the biblical text, in the seventh century, they supplied that protecting hedge which, according to Rabbi Akiva's saying, the Masorah was to be for the words of the Bible. Punctuation, on the one hand, protected the tradition from being forgotten, and, on the other, was the precursor of an independent Bible science to be developed in a later age.