What rationale do the Rabbis use when differentiating amulets from recognized forms of idolatry?

Question

The use of amulets for healing and protection has a long history in Judaism. I know that we are warned against idolatry when it comes to foreign worship practices around objects. (Prayer beads, Pagan stone practices, etc.)

My question is what is the rationale used by the Rabbis in determining that amulets and other forms of Jewish practice (Say the red string in Kabbalah practices) are acceptable and different?

Is it purely the intention being rooted in Hashem and Torah or is it something else entirely?

What is the line that separates a common Jewish practice from something the Rabbis consider more dangerous?

Answer 1

A source to start with is Shabbos 67a-b, where R. Meir allows certain practices that have no natural basis, while the Chachamim forbid them as darkei ha-Emori, the ways of the pagan Amorites. The Gemara there lays down a basic rule, which is accepted as halachah (Shulchan Aruch, Orach Chaim 301:27):

כל דבר שהוא משום רפואה אין בו משום דרכי האמורי

Any practice which is done for healing purposes is not prohibited on the grounds of darkei ha-Emori.

(Shulchan Aruch there adds that any kind of spell (לחש) is also permissible, whether for healing purposes or not, unless it's been tested and found not to work.)

I haven't found any of the commentaries offering a rationale why all healing practices should be permissible. But it may be simply that, after all, the mechanism of action of "naturalistic" cures isn't always known either (more so back then, but there are still some cures today of which this is true), so that there's not such a sharp distinction between "naturalistic" and "non-naturalistic" ones.

(Another angle on that last point, actually: even when the mechanism of action of a given cure is known, we still know that it is Hashem Who makes it effective. To just trust in the doctor and his medicine would in fact be a form of idolatry. The same, then, must be the case when using an amulet or whatnot - it's not the amulet itself that heals, it's that the user trusts that Hashem will make it do so.)

Answer 2

I am quoting an excerpt of "Jewish Magic and Superstition" by Joshua Trachtenberg (1939) found on pages 143-144 (titled "Preparation of Amulets"):

The popular addiction to this form of magic was so strong that it was futile to prohibit altogether the use of amulets on the Sabbath, and instead a set of rules was created which distinguished between effective and "approved" (literally, "expert, experienced") amulets, which might be worn on that day, and those technically classed as unapproved. According to these rules, an amulet prepared for a specific function, which had been successfully employed by three different persons, was "approved" as equally effective for all, and an expert who had written three different amulets which had been tested by three individuals was himself "approved," and the products of his skill were permitted to all. Such amulets might be worn on the Sabbath, others not. These principles were established in the Talmud, and were frequently reiterated in the medieval literature. Medieval authorities were willing to forego a test in the case of recognized physicians: amulets written by a "rechter doktor, der gewiss is’, un’ gedoktrirt is’" were automatically "approved" as coming within these provisions. Their necessity was explained in this wise: were the effectiveness of the amulet, or the writer, to rest solely upon a test made in a single case, the cure might be attributable to the "star" of the patient or physician, rather than to the amulet itself. None the less, however insistently these rules were repeated by the rabbis, popular observance was lax. Even the authorities did not forbid the wearing of "unapproved" amulets on weekdays, though this was the subtle purpose of the legislation, and the rabbinic responsa indicate that they were freely worn on the Sabbath as well. The lust for miracles was more compelling than religious scruple, and rabbinic regulation of the amulet industry was as often honored in the breach as in the observance.

As sources he lists Toss. Shab. V, 9, 10; Shab. 61a-b, 115b, and Rashi, 61a; J. Shab. 7c, 8b.

I'd highly recommend to read the Amulet chapter in it's entirety.