Sources of Halacha

The Rambam in his introduction to Mishna Torah explains that the purpose of his writing the Mishna Torah was to codify the halachos of the Torah She'baal Peh. He thus went through all the sugyos in Shas Bavli and Yerushalmi and determined the final halacha in each case and recorded it. The Bais Yosef in his introduction explains how he codified the halacha. He first determined the opinions of the Rambam, the Rif, and the Rosh. He then followed a majority to determine the halacha. Of course, this approach of the Beis Yosef favors the Sefardim (for two of the three he relied upon were Sefardi) and, thus, we have the hagahos of the Rema on the Shulchan Aruch.

The Rif and the Rosh, like the Rambam, essentially wrote seforim that recorded the maskanos of the sugyas hashas. Thus, "halacha" really should be nothing more than the maskanos of the gemara. This approach would end up completely ignoring sources in Sifrei Kabbalah, like the Zohar.

In fact, the Chasam Sofer in Orach Chaim at the end of Siman 51 writes that anyone who mixes Kabbalah into Psak Halacha, it is a forbidden mixture (like shaatnez or kilayim). This would seem to be consistent with what we wrote above.

In reality, however, this does not seem to be the case. Both the Bais Yosef and the Magen Avraham are filled with citations of the Zohar, despite the fact that they are both sifrei halacha. How do we reconcile this fact with the statement of the Chasam Sofer?

This issue is dealt with by the Shevet HaLevi in Chelek Alef Siman Bais. He essentially says that even the Chasam Sofer would admit that kabbalah can make its way into halacha, and the Chasam Sofer's statement is only to be applied in limited situations. You can check yourself for the details of his answer.

Finally, the Mishna Berurah in Siman 25:42 quotes the Knesses HaGedolah on this issue. Here is a rough translation:

The Knesses HaGedolah writes that in terms of the rules of psak: any time the baalei kabbalah and Zohar argue on the Gemara and the Poskim we follow the Gemara and the Poskim. However, if the Baalei Kabbalah are machmir one should be machmir as well. And if the issue isn't mentioned in the Gemara and the Poskim even though it is mentioned in Kabbalah we cannot force someone to be noheg like that. And a din that is not mentioned the opposite way in Shas one should follow Kabbalah. And also, in a place where the Poskim argue one can use the words of Kabbalah to be machria.