ואין אדם דן גזירה שוה לבטל תלמודו ("From a gezerah shavah conclusions may be deduced which support tradition, but not such as are opposed to tradition"; comp. Maimonides in the introduction to his Mishneh Torah). The words of the text which form the basis of the deduction from analogy must be free, i.e., they must be superfluous and non-essential, or they may not be used (מופנה להקיש ולדין הימנו גזירה שוה). This limitation of the gezerah shavah, however, to superfluous words is not generally recognized. Akiva considers the gezerah shavah valid when neither of the two words is superfluous (אינו מופנה כלל). According to Rabbi Ishmael, it is sufficient if the analogy is free on one side (מופנה מצד אחד), i.e., if one of the two words forming the basis of the analogy is pleonastic. Rabbi Eliezer alone requires both words to be superfluous. Binyan ab mi-katuv echad (בנין אב מכתוב אחד) In "binyan ab mi-katub echad" ("A standard from a passage of Scripture") a certain passage serves as a basis for the interpretation of many others, so that the decision given in the case of one is valid for all the rest. Binyan ab mi-shene ketubim (בנין אב משני כתובים) By this rule of "binyan ab mi-shene ketubim" ("A standard from two passages of Scripture") a decision in two laws having a characteristic in common (הצד השוה) is applied to many other laws which have this same characteristic. Rabbi Ishmael unites rules 2 and 4 in his third rule, while the same combination forms the eighth rule of Rabbi Eliezer. Kelal u-perat and perat u-kelal (כלל ופרט ופרט וכלל) The rules of "Kelal u-perat" and "perat u-kelal" ("General and particular, particular and general") is a limitation of the general by the particular and vice versa. According to Rabbi Ishmael, this principle has eight special applications, and thus includes eight separate rules in his scheme (Nos. 4-11). This method of limitation is one of the main points of difference between Ishmael and Akiva. According to the former, who follows his teacher Rabbi Nehunya ben HaKanah, the particular is only an elucidation of the preceding general expression, so that the latter includes only what is contained in the particular (כלל ופרט אין בכלל אלא מה שבפרט). But if still another general follows the particular, the two general expressions are defined by the intermediate particular, so that the law applies only to