Question

Good evening,
I looked a bit yesterday in the book, and with your permission I have several comments.
On p. 106 you wrote that, according to Maimonides’ method of classification, he should have composed one book with all the Torah-level laws according to the 613 commandments, and another book on the rabbinic laws grounded in “do not deviate,” except that such a book would have been impractical. (My wording.)
According to Maimonides, when the Sages added decrees, did they remain merely decrees dependent on “do not deviate,” or are they considered an extension of the original commandment? For example, the prohibition of secondary forbidden relations is by virtue of “do not deviate,” but one could perhaps say that the Sages have the power to expand the Torah’s forbidden relations, so that one’s mother’s mother is an extension of one’s mother and one’s mother’s mother.
And perhaps this depends on the dispute whether for every rabbinic commandment we recite “Who has sanctified us with His commandments and commanded us” regarding the commandments of the elders, or whether we recite the blessing over the specific commandment.
I understood from what you wrote on p. 108 that rabbinic prohibitions are fences and safeguards so that one will not come to violate a Torah prohibition. Enactments can also apply to positive commandments, such as Hanukkah and taking the lulav all seven days. Maimonides wrote in the Laws of Tzitzit, chapter 3, law 2:
But a garment made of other materials, such as silk garments, cotton garments, camel wool garments, rabbit wool, goat hair, and the like, is obligated in the commandment of tzitzit only by rabbinic law, in order to be careful regarding the commandment of tzitzit.
Is this a decree? It does not seem so much that it is, since tzitzit is a positive commandment, and also from the passage in tractate Menachot it appears that they did not decree regarding neglect of the commandment of tzitzit, except lest one wear wool-linen mixtures, but that is not the topic here. And Maimonides’ wording here, “in order to be careful regarding the commandment of tzitzit,” is distinctive—not a decree lest one fail to place tzitzit also on wool and linen, but perhaps to give a person another opportunity to remember God’s commandments (though if so, it is difficult why a leather garment is exempt from tzitzit). I did not find anyone who comments on Maimonides’ wording.