Are ethics and morals [I will be using these terms interchangeably because I still haven't figured out the difference between them] autonomous or heteronomous? Meaning, should they come spontaneously from the inside of a person [as Kant famously held] or from an outside source [such as G-d]?
I am going to present various sources without extensive analysis בל"נ [and am using the sefer הלכה בימינו to help]:
Rav Saadiah Gaon [אמונות ודעות תחילת מאמר ג]:
כי השכל מבחין בגניבה, ואין בו איך יהיה הממון ברשות האדם עד שיהיה קונה לו, מדרך הסחורה, או מדרך הירושה, או מדרך ההפקר, כמו ציד הבר והים, או בתת הדמים יתקיים המקח, או בתפישתו המקח, או בדיבור בלבד, ושאר מה שייפול בשער הזה מן הספקות, שהוא ארוך ורחב, ובאו הנביאים בכל דבר מהם בדין פוסק.
The intellect understands that one can't steal. For that we need no outside source. The Torah has to tell us the details of what exactly is considered stealing. For example: Borrowing without permission is halachically considered stealing. people wouldn't necessarily know that on their own.
Another example: Murder. The intellect knows that murder is evil but what about abortion? is there any difference between stages of pregnancy? Is embarrassing someone tantamount to murder? I would ssay no. The halacha says yes.
So too a point ethics and morals are autonomous but then we need Hashem to fill in the details.
Rabbeinu Bechaye adds in Chovos Halevavos that total dependence on the intellect alone is dangerous because the intellect can mislead one. [Machlokes Rabbeinu Bechaye and lihavdil, Kant:-)].
The Kuzari also says that you can't rely on your own reasoning:
(ז) אָמַר הֶחָבֵר: הַמַּעֲשִׂים הַמִּנְהָגִיִּים וְהַחֻקִּים הַשִּׂכְלִיִּים הֵם הַיְדוּעִים, אֲבָל הָאֱלֹהִיִּים הַנּוֹסָפִים עֲלֵיהֶם לָחוּל בְּאֻמַּת אֵל חַי שֶׁיַּנְהִיגֶנָּה, אֵינָם יְדוּעִים עַד שֶׁיָּבֹאוּ מֵאֶצְלוֹ מְפֹרָשִׁים וּמְחֻלָּקִים. וְעוֹד, כִּי אֵין הַמִּנְהָגִיִּים וְהַשִּׂכְלִיִּים הָהֵם יְדוּעִים, שֶׁאִם נֵדָעֵם בְּעַצְמָם לֹא נֵדַע שִׁעוּרָם, כִּי אֲנַחְנוּ יוֹדְעִים שֶׁהַעֲנָקָה חוֹבָה, וּמוּסַר הַנֶּפֶשׁ בִּכְנִיעָה וּבְשִׁפְלוּת חוֹבָה, וְהַהוֹנָאָה מְגֻנָּה, וְהַהֶפְקֵר עִם הַנָּשִׁים מְגֻנֶּה, וְהַבִּיאָה אֶל קְצָת הַקְּרוֹבוֹת מְגֻנָּה, וְכִבּוּד הָאָבוֹת חוֹבָה, וְכַדּוֹמֶה לָאֵלֶּה, אַךְ הַגְבָּלַת זֶה וְשִׁעוּרוֹ עַד שֶׁיִּהְיֶה טוֹב לַכֹּל, אֵינֶנּוּ כִּי אִם לֵאלֹהִים יִתְבָּרָךְ. אֲבָל הַמַּעֲשִׂים הָאֱלֹהִיִּים אֵין שִׂכְלֵנוּ מַגִּיעַ אֲלֵיהֶם [וְהֵם] (נִדָּחִים) [נִדְחִים] אֵצֶל הַשֵּׂכֶל, וְהֵם נִשְׁמָעִים כַּאֲשֶׁר יִשְׁמַע הַחוֹלֶה אֶל הָרוֹפֵא בִרְפוּאוֹתָיו וְהַנְהָגוֹתָיו. הֲלֹא תִרְאֶה הַמִּילָה, כַּמָּה הִיא רְחוֹקָה מִן הַהַקָּשָׁה וְאֵין לָהּ דֶּרֶךְ אֶל הַהַנְהָגָה, וּכְבָר קִבֵּל אוֹתָהּ אַבְרָהָם, עִם קְשִׁי הָעִנְיָן עַל הַטֶּבַע, וְהוּא בֶן מְאַת שָׁנָה, בְּנַפְשׁוֹ וּבְבָנָיו, וְהָיְתָה אוֹת בְּרִית לְהִדָּבֵק בּוֹ וּבְזַרְעוֹ הָעִנְיָן הָאֱלֹהִי, כְּמוֹ שֶׁאָמַר: וַהֲקִמוֹתִי אֶת־בְּרִיתִי בֵּינִי וּבֵינֶךָ וּבֵין זַרְעֲךָ אַחֲרֶיךָ.
The Rabbi: The social and rational laws are those generally known. The divine ones, however, which were added in order that they should exist in the people of the 'Living God' who guides them, were not known until they were explained in detail by Him. Even those social and rational laws are not quite known, and though one might know the gist of them, their scope remains unknown. We know that the giving of comfort and the feeling of gratitude are as incumbent on us as is chastening of the soul by means of fasting and meekness; we also know that deceit, immoderate intercourse with women, and cohabitation with relatives are abominable; that honoring parents is a duty, etc. The limitation of all these things to the amount of general usefulness is God's. Human reason is out of place in matters of divine action, on account of its incapacity to grasp them. Reason must rather obey, just as a sick person must obey the physician in applying his medicines and advice. Consider how little circumcision has to do with philosophy, and how small is its social influence. Yet Abraham, in spite of the hardship the very nature of this command must have seemed at his age, subjected his person and children to it, and it became the sign of the covenant, of the attachment of the Divine Influence to him, as it is written: 'And I will establish My covenant between me and you and your seed after them in their generations, for an everlasting covenant, to be a God unto you . . .' (Genesis 17:7).
