Rabbi Shimon ben Yochai of the Mishna says you go by the reason for a mitzvah to see if the mitzvah applies. דורשים טעמה דקרא

Rabbi Shimon ben Yochai of the Mishna says you go by the reason for a mitzvah to see if the mitzvah applies. דורשים טעמה דקרא

And the Sages say you don't.

It is known that there is a contradiction in the Rambam [Maimonides] if we go by R. Shimon or the Sages.
 And this came up in Bava Metzia but I never got there with my learning partner so I never learned that subject with any depth.
But I thought to at least lay out the basic subject for public information.
In Bava Metzia this comes up about the widow. לא תחבול בגד אלמנה"Thou shalt not take a garment of a widow as a pledge for a loan." R. Shimon] says if she is not poor you can take a pledge [because we go by the reason for the verse. Even though the verse don't take a pledge from a widow still we know the reason for this is because of compassion for her poor state. If she is not poor there is no reason not to take  a pledge.] [Notice we do not say there is any mystical reason for the mitzvah. Even the sages agree that we know the reason for all the mitzvot except for just one. The only argument is if we go by the reason or by what is written.]
Here the Rambam goes with the Sages. But by the prohibition of marrying a woman that serves idols the Rambam goes by the reason and not by what is written.
I thought the Rambam had an idea of the reason modifying how we apply the mitzvah because of what he wrote in the commentary on the Mishna.
But then I saw Rav Shach [of the Ponovitch Yeshiva in Bnei Brak] wrote about the law in the Rambam about a city of idolaters on the border of Israel, that even Rabbi Shimon agrees that the only question is if the mitzvah applies in a certain situation or not. We never use the reason to modify the rules.
The law in the Rambam is Laws of Idolatry 4:4. A עיר הנדחת  If a city of idolaters is on the border of Israel we don't destroy it so that the border should not be left open. That reason is to R Shimon. From this Rav Shach proves his point you don't modify the law based on the reason for the law.
The idea here is how you would apply the law here would be different if we went by the Sages--which we do. So the Rambam bringing the reason of RS is not meant to modify it.

[I have depended on RS even though he is not the halacha, because I consider my situation to be שעת הדחק  emergency. We use the same logic for other things like new produce  חדש. We say We can depend on R Eliezer in an emergency. This is even though clearly the halacha is not like him. This gives rise to the fact that I sometimes take any opinion mentioned in the Gemara as my rule. In fact I have used the Gemara as my personal code of law --ever since my entire situation became a state of extreme emergency. But because the world is messed up I thought I should tell others because there could be other people out there that also find themselves in situations that are hard and can't be as strict in law as perhaps we all should be. What makes my situation to be  what I think is a emergency is the group of people that normally I would try be fit in with--the group that tries to keep the Torah-had been taken over by the Dark Side, the Sitra Achra, as is well known. So if I or anyone else wants to keep the Torah we have to do it on our own and and say as far as possible from those that make a display of keeping Torah. Hasidim work for the exact opposite of what they claim. In this world nothing is what it seems.]

I should mention that there are people that do not consider going through an intermediate as a problem. There are groups that think this is OK. But I think the Torah is right that this is a problem. I dont know why people ignore the Torah in this detail, but to me it seems like a serious matter.With the vav they were joining G-d with the Golden Calf

Is "joining" שיתוף (Joining something to G-d) more serious than idolatry or less?
This is an argument between R Meir of the Mishna and R Shimon Ben Yochai

But the Rambam seems to make an amalgamation of the two opinions.
The argument is in Sanhedrin 63.
R Meir said, "If not for the letter vav in 'These are your gods,'
(which was said to the Golden Calf) Israel would have been liable to be destroyed."
[The vav makes it plural. Without it it would have been "This is your god" referring to teh Golden Calf. With the vav they were joining G-d with the Golden Calf]
R. Shimon said, "But anyone who joins the name of God with something else is uprooted from this world as it says 'to God alone.' Rather the vav is to tell us they desired many gods." [In Avoda Zara it is explained that that means they accepted the Golden Calf but were open to accepting other god also. But they did not join God with the Golden Calf. And if they had that would have been worse.  ]

The Maharsha says that joining is what the Rambam describes at the beginning of the Laws of Idolatry. And there the Rambam says the main idea of idolatry was they saw that God put the stars in Heaven so it is his will that we should honor them just like he honors them, and by that they will be advocates for us. [The Rambam  goes into detail about this also in his commentary on the Mishna. This is known in the  as the problem of the אמצעי intermediate. That is people know God is the creator but they feel they can't approach Him directly so they go through a middle step like a person or anything else to serve as a middle step.]
Then the Rambam says  the actual idolatry that we know came after that. It seems the rambam is saying the later step was worse. That is the אמצעי (emtzai) (using an  intermediate) is less serious.

But then when you look at the Rambam about actual שיתוף joining --in the only place he actual brings up our Gemara-he says one who swears by God and something else will be uprooted--that is the opinion of R Shimon. Not like R Meir!

So what we have here is what seems like a contradiction in the Rambam.
I should mention that there are people that do not consider going through an intermediate as a problem. There are groups that think this is OK. But I think the Torah is right that this is a problem.
I don't know why people ignore the Torah in this detail, but to me it seems like a serious matter.
I don't mean to be critical of any tzadik. But even a tzadik  should not be an intermediate.

When I read  the introduction of Maimonides to the Mishna, I was surprised to see that he had already at the beginning of his life laid out his plan about what he was going to write. He already had the basic outline of the Yad HaChazaka (Mishneh Torah) and the Guide for the Perplexed already laid out in his mind.
This reinforced what I was anyway thinking about the Rambam that his switch to Aristotle was intentional and meant to clarify the issue of idolatry. He meant it from the beginning, and it was not some fluke at the end of his life.

He wanted the difference between idolatry and Monotheism to be sharp and distinct and not dependent on degrees. Of course you could ask who does not want that? Everyone wants that! But my point is no one could get it. With Nachmanides or any Neoplatonic system, it is completely arbitrary where you draw the line between godliness and not godliness. Obviously the Rambam meant right from the beginning to stamp that out.
As long as you believe in Emanation, then anything you want can be godliness. And you can conveniently say the line stops where you want it to stop so that your system is conveniently kosher and everyone else's is not.  Perfect. [I don't claim that was the only reason the Rambam switched to Aristotle. The Neo Platonic systems had anyway been tried and failed. I don't recall what the problems were off hand. Maybe the third person problem was one thing.(Which is only a problem if you consider substance to be not a composite.)]

At any rate, we do have Nachmanides with his Neoplatonic approach, which does tend to balance the playing field.

And this leads to the question about שיתןף "joining" in Tosphot Sanhedrin 63b.

 I am not sure what that Tosphot means. He says one can have a business with Christians because of 1) when  they swear by their holy things, they don't intend godliness, 2) when they mention Jesus, they intend the Maker of heaven, 3) they are not commanded about "joining."
So far I have not been able to make heads or tails about what Tosphot means here.

I am guessing that maybe in the Middle Ages people would swear by the wafer. The second thing seems to be dealing with the Trinity of Athenius.  The third thing seems to be some kind of idea about Emanation because otherwise why would they not be commanded not to do joining?

And it is hard to know why Christianity would be "joining" שיתוף. Joining we know from page 63a means to join something else to God. What Christians do is say x=y. That is not the same as x+y.

Appendix:
1] I should mention just to clarify that saying someone is the son of God is not a problem because the Torah does this all the time.  בנים אתם להשם אלהיכם, שלח את בני ויעבדני, בני בכורי ישראל "You are the children of the Lord your God," "Send out my son so that he will worship me." "Israel is the first born of God." "My son, my first, born Israel." So if all the Jewish people are children of God, then specifying one particular member of the entire set as a son of God is not an exception to the rule.
So if your father says, "These three boys are my children" and then says "This boy [who is in the set of all three boys] is my son," there is no contradiction because he was already part of the entire set.
2] Tosphot is not referring to Roman Catholic doctrine after Aquinas. Rather to pre-Aquinas doctrine which was Neo-Platonic.
3] We can see why pantheism would be a problem. Not only is it not what the Torah is saying, but also it has this aspect that the Rambam did not like about  Emanation. [To the Rambam there is no emanation.]
4] To the Rambam God is the First Cause. He is not a composite.
5] It is not just that I do not understand the individual points of Tosphot. It is also I don't know how he is combining his points.
6] We find for example that the Ari considers the souls of people like the patriarchs to be from the world of Emanation. And that we know from the Zohar and the Ari is Godliness. To the Ari the bottom of Emanation is where godliness ends and creation begins. That is explicit in the Zohar. And in the Shaar HaGilgulim of the Ari and Reb Chaim Vital we find this theme extended greatly. We find even Bava Sali said about his son, Meir Abuchatzeira that his soul was from Emanation. So it is not unusual to claim someone is Divine. No one considered it even to be a theological problem. Mainly because people form their ideas based on group identity, and not because they actually think about the implications of their beliefs.
7] So the venues of future exploration are the Gemara in Suka and the other Tosphots that bring up this issue.   The Gemara in Suka asks on the Mishna the question of "joining."
8] My own opinion I should mention is like that of the Rambam. God is one, not two and not three, and not a composite. And I don't think anyone's soul is Godliness. But I am willing to accept that some people are divinely inspired like Moses and the prophets.

) Stay away from doctors.
) Stay away from psychologists.
) Stay away from people that present themselves as teaching Torah. (There are not many exceptions but the heads of Lithuanian yeshivas are exceptions to this rule in that they in fact are just teaching Torah.)

)They are all false healers, and are put on earth in order to make people sick. Doctors are here to make people physically sick. Psychologists to make people mentally sick. And people that teach Torah are to make people spiritually sick.

) Learn Torah in the straight Lithuanian Yeshiva Path. Gemara, Rashi, Tosphot.

) Go to a forest to talk with God (This is hard in NY, and easy in Safed. If you are in NY, and no forest is around, just being in your room alone and talking with God is also good.)


) Learn fast. Very fast. Say the words quickly in order and go on. I have used this method for years but also learned in ways that I think applied to me. For example I have a learning partner which is a prime axiom in the Litvak world.  Also when I was at Polytechnic, I said the words forwards and backwards because I was under pressure to pass exams. I could not rely on the idea I would eventually read the material again. I had to know it then and there.
For myself I also combine ideas from my parents,  the Rambam, the Gra and Rav Shach.  I am not saying my path is anything anyone else would agree with. It is just that it works for me.

I notice that sometimes I bring up this small paragraph in the Talmud about the argument between Rabbi Meir and Rabbi Shimon Ben Yochai and it seems to make some people uncomfortable. The basic idea is simple. R Meir said they said to the Golden Calf, "These are your gods Oh Israel which brought you out from Egypt." If they had said "This is" they would have been destroyed. R. Shimon said But anyone who joins the name of God with something else is uprooted from this world . So it must be they desired many gods.
This statement of R Shimon has two possible meanings. One is that joining is worse than idolatry. But then there would be a question from the verse he brings as a proof "Only to God."
Or he means idolatry and joining are equal but they did not accept the Gold Calf but just desired it. But then we have a question from the verse where they said "these are your gods."

The reason I think that people don't like to her this is because "joining" is a delicate point.

For one thing sometimes a person is following some great leader--and in fact that leader is great, or sometimes there are following someone who is not great. But in both cases they are adding something to God. So when I mention this particular small paragraph it makes them uncomfortable.

There is a limit to sexual freedom from the standpoint of the Torah. Reform Judaism is admirable in many ways but in this issue I think they are going against the Torah.
The right aspects of Reform are its support of Israel and recognition of the importance of laws of the Torah between man and his fellow man. And my family in fact went to Temple Israel of Hollywood and that is where I had my bar mitzvah. But Reform is not careful enough when it comes to laws between God and man. In any case, I would still attend only Temple Israel as that was the place my parents decided was right for us. But personally I would try to be more careful about the laws of the Torah.
In any case, when I decided to learn Torah I went to NY, and was very happy with the Lithuanian yeshiva world. But if I was in LA, I still would go only to Temple Israel,  [and avoid the insane religious world  there like the black plague.]
[I was a few years in Shar Yashuv Far Rockaway, NY which was an amazing place. And later at the Mirrer Yeshiva which was better than an LSD trip.] OK that is maybe not the best metaphor. Let's just say the Mir was a stupendous  place for the few years I was there. And I think that anyone who wants to have an idea of what the Torah is about also should attend a straight Litvak place for at least four years.[Which was the time I was at the Mir.]
I should mention for the general public that the normal time frame of a Lithuanian yeshiva is in fact exactly four years. You go through  four levels until the top class. But the actual cycle of a Litvak yeshiva is seven years--for the three Bava's  and Ketubot, Gitin, Kidushin and Yevamot.

[For me everything got mixed up because in my switch from Shar Yashuv to the Mir I ended up in Far Rockaway in the middle of Yevamot   and I had just finished Ketubot. Then when I got to the Mir they were doing Nedarim for Elul and then started Ketubot. So I joined the Shabat group. That was a small group that were doing Shabat.] 

It is hard to figure out what R. Shimon ben Yochai is saying in Sanhedrin 63.
There is one question because the verse he brings does not distinguish between "joining" (שיתוף) and regular idolatry בלתי להשם לבדו [To God alone].

So let me lay out the basic paragraph and then I will say over the problems.

 Rabbi Meir said, "If not for the letter "vav" in 'these are your gods, O Israel, which brought you out from Egypt,' the Jewish people would have been destroyed."

R Shimon said, "Anyone who joins the name of Heaven with something else is uprooted from this world. Rather it means they desired many gods."

What it seems at first glance  is this. It would not have mattered if they had done pure idolatry or joining--in any case they would have been destroyed. Rather they only desired other gods. This makes sense. But then what do we do with the fact they said, "These are your gods Israel." They did more than desire. They accepted.

So now we understand why Rashi said in fact just that: They accepted other gods. But then what is R. Shimon saying?

Now just to be clear, the verse בלתי להשם לבדו "To God alone" is from the verse "He who sacrifices to the gods will be destroyed,.. only to God alone." Exodus 32. That is: One must not sacrifice to the gods, only to God. This does not distinguish between to other gods and to other gods with God. As far as this verse is concerned it is all the same thing. One must sacrifice to God alone, and anything else is bad.

And I hoped to get insight by opening up the Talmud in Suka 45b. But so far I have gotten nowhere.

What I had thought at first is R. Shimon is saying joining something with God is worse than straight idolatry. And if that was the case, everything would be OK except the verse "To God alone." --which has one complete set of services towards God alone--and everything outside that set is not OK.

This is relevant modern day issues because Christianity is considered by Tosphot to be "joining" [Sanhedrin 63b].  That is Tosphot thinks Christianity is joining someone to God. But then he says gentiles are not commanded against this. But why not?
In any case, it looks to me that Tosphot is right because even Thomas Aquinas has trouble getting past the idea that the physical body of Jesus was God. I forget his answer but at the time I read it, it did not sound very convincing. I will leave that to  modern Scholastic Scholars like Feser.