Overview: A rational approach to the supernatural elements mentioned in the Talmud, including the “Evil Eye,” the existence of demons, and alleged superstitions, and whether they are real and why they are not observable.
The Evil Eye (Heb. ayin hara), demons (Heb. sheidim), and superstitions (defined here as the belief—irrespective of whether it’s true or not—in supernatural forces working as a result of our actions; Heb. segulos) are all supernatural elements that manifest into the physical nature. They are common in almost every religion nowadays and were even more prevalent back in history before the scientific understanding of the world developed. As an example, before the science of bacteria was discovered, it was common to believe that infections and chronic diseases were the result of demons and other supernatural causes that haunted the sick person.
Judaism, starting from early sources such as the Talmud, contains elements of these supernatural ideas (i.e. the Evil Eye, demons, and superstitions) as well. The question is, whether we, with our current understanding of science and our rational approach to nature, should accept these statements of old.
Is the Evil Eye a real threat? Did and do demons actually exist? Are the superstitions real? Why can’t we see their effects clearly? Has the Talmud (as well as later Jewish sources) adapted (some of) these concepts from the surrounding cultures?
These are all very fair questions that many people grapple with yet are afraid, for good reasons, to discuss them out of concern of being labeled a heretic. But Judaism must be transparent in order to survive in this day and age and such questions must be confronted.
The Evil Eye
The idea of an Evil Eye has been applied, in our vocabulary, to a wide-ranging field including all superstitions. However, the more accurate definition is much more limited. The earliest mention of the term ayin hara is in Mishnayos[i] and its meaning is someone who has a negative worldview and is constantly jealous of others. In contrast, ayin tov (the antonym of ayin hara) means someone who has a positive worldview and is happy with their lot in this world. Judaic theology is that when someone views (and most certainly speaks of) someone else negatively, they are actually harming that person by casting an evil spell on them. This concept is the more accurate definition of the Evil Eye—the potential harm caused by negative and jealous people on those who they are jealous of.
This concept has strong roots in Judaism.[ii] Even the Written Torah clearly discourages counting of the Jewish people because it may cause harm[iii]—the earliest source for the Evil Eye. As a result, different customs arose as precautions that would avoid getting into such a situation of making others jealous. An example would be the widespread custom not to publicize (beyond immediate family) that someone is pregnant out of concern of health issues arising as the result an Evil Eye. Another example is the common usage of the term “bli ayin hara” or “kein ayin hara.”
A very related concept is that our verbal words affect the future to some extent. Therefore many Jews will refrain from saying negative things, even if in a joking manner. Many will say “chas ve’shalom” (eng. G-d forbid) following a negative statement.
A much more interesting topic is the subject of demons, or sheidim, frequently brought up throughout Talmudic discussions. Understandably, there’s tremendous skepticism about the reality of demons having ever existed.
While the majority of Jewish rabbis accepted the reality of demons, a notable exception is the Rambam[iv] (among others[v]). He outright denies the existence of any supernatural elements (beyond the physical nature that G-d created) controlling this world. He believes that all statements mentioned in the Talmud about the power of the constellations, witchcraft, demons, and superstitions were errors made by some Talmudic sages who mistakenly adapted widespread ideas of the world at that time.
While this rationalist view might seem tempting at first, it argues with many Talmudic sources[vi] and more importantly it fails to explain some biblical accounts. The Talmud is full of tales that include the power of sorcery—well beyond the force of physical magic. It would be hard to categorize these stories as mere metaphoric Aggadah (see chapter “Did the Wild Stories of Midrash Actually Happen?”) because they are often brought in the context of Halacha. Perhaps the greatest obstacle for this position is I Samuel 28:7-20 which recounts the story of King Saul and his use of witchcraft to contact the deceased Prophet Samuel.
The opinions that say demons did exist, will admit that they became extinct over a period of time. Their presence in this world (at least in a visible sense) became more and more limited over the generations. They are said to have been fully extinct about 350 years ago by the decree of a powerful saintly Rabbi, Rabbi Yoel Baal Shem.[vii]
It is also possible that while demons did exist, their significance and their impact may have been overblown in the Talmud by some sages who were influenced by common belief at the time. This means that after embracing the reality of the existence of demons, some sages may have attributed certain powers to them and have developed various superstitions in order to avoid harm from the demons. Many things could have been associated with demons simply out of understandable scientific ignorance at the time.
This explains why the Babylonian Talmud puts more emphasis on demons than the Jerusalem Talmud. The idea of demons was prevalent in Babylonian folklore and it made its way into the Jewish lifestyle.[viii] Am I a heretic for suggesting this possibility? In light of the Rambam’s view stated earlier, I’d say not. Also see chapter “Can the Rabbis Make Errors?”
As briefly mentioned earlier, we will use the term “superstition” here not in its common usage that refers to false beliefs in alleged supernatural omens and spells. We use the term as a general reference to the belief in supernatural effects happening as a result of physical actions of ours—irrespective whether they are true or not. We use this word for lack of any other singular word to bring out this idea. In Hebrew this is generally referred to as segulos (both positive and negative segulos).
Because barely any rabbinic sources speak about this topic from a critical approach, the subject is left for much discussion. In my opinion, it would be unfair to categorize all superstitions as categorically true or categorically false. It’s a pool of confusion that as a whole can be categorized into three distinct categories. It would be exceedingly difficult to map out which segulos and superstitions go into which category; but these three categories exist and it is uncertain, at least to me, into which category specific ones fall into. The three categories are:
(1) Those segulos and superstitions that true and real. However, many of them are not to be taken to their extreme literal wording. For example, the Talmud states that whoever is careful with the Mitzvah of lighting Shabbos candles, will merit to have wise children who study Torah.[ix] Of course this cannot be taken to its extreme because we see clearly that this is far from always being the case. In fact it is hard to see a correlation between those being careful in lighting Shabbos candles and those meriting to have wise and learned children. Obviously, then, the intention was that one who is careful about lighting Shabbos candles, will have an extra merit—i.e. more of a chance—of being gifted with smart and learned children. However, there are many other factors that enter the equation before someone is or isn’t merited with a blessing. This applies to every single segula and superstition. 
These segulos come primarily from ruach hakodesh, the divine revelations revealed at times to holy sages.
The Talmud says regarding a specific superstition that “one who is not troubled by it, will not be troubled by it.”[x] This means that one who isn’t concerned about these specific segulos will not be affected by it. Only those who are particularly concerned with the segulos, will they have a spell on. This concept was broadened to many (and perhaps all) ayin haras (including superstitions) by later great rabbis.[xi]
Many of us have the tendency to delegitimize any segula or superstition simply because we despise them as a whole because of all the made-up ones. However, this attitude can be deceiving if it interferes with our relation to real superstitions. Just because most are fake (see upcoming category #3), doesn’t mean that we should dismiss all of them in our mind.
(2) Those that were true at one point but later changed. The Talmud contains many remedies that no longer work with the modern human body. Throughout the generations, our bodies went through a natural evolution that changed the physics of our biology. As a result the nature of medicine also evolved and what worked on bodies of two millennia ago may not work on the body of the twenty-first century.[xii]  This same concept refers to many segulos and superstitions which are explained to be the reflection of our physical nature. Just like our bodies changed tremendously throughout the ages, so has the effects of segulos and superstitions changed. Mainly segulos of medicinal elements are included in this category.
An example of this might be the superstition of the Talmud to not do things in pairs[xiii] out of concern of demons harming us. Nowadays, when demons no longer exist on a practical level, this superstition isn’t kept and in fact isn’t mentioned anywhere in Halacha.
(3) Those that aren’t and never were true segulos and superstitions that actually work. This includes most modern alleged segulos for shidduchim and parnasah and whatever else it may be. This also includes many segulos documented in the Talmud as they weren’t written out of ruach hakodesh but were merely recording the common thought of the time that dominated the surrounding cultures. Many segulos and superstitions are visible that they were influenced by the Egyptian, Greek, Babylonian, and Persian cultures.[xiv]
Of course, this belief isn’t heretical and in fact the Rambam takes a far more extreme approach brought earlier. Similarly, being that segulos and superstitions are included in the category of Aggadah, they can bare mistakes or be the opinion of an individual—as discussed in chapter “Did the Wild Stories of Midrash Actually Happen?” where we quote sources for this concept that might sound novel to some.
It would be hard to estimate how many or which segulos and superstitions are included in this category, but my personal opinion is that there’s quite a lot in this class. It is only reasonable to assume that the Jewish sages would adapt things from their neighbors and we indeed see that they shared ideas such as astrology and means of preventing demons. I think it will be futile to mention specific examples, because individual cases can always find defenses. But a general trend is seen that many superstitions were adapted from neighboring cultures.
There are many non-Jewish superstitions that creeped their way into the Jewish community. They have no sources in authentic Jewish literature.
[There is a commonly cited Rashba that says that we should respect/keep any minhag (eng. custom) that is done even by the elderly grandmothers and it is heretical to mock their baseless customs. But this alleged citation is grossly exaggerated and taken out of context. The quote can be found in Tshuvas HaRashba 1, 9. The context there is that a philosophical argument, for example ones against the Revival of the Dead (Heb. techiyas hameisim), shouldn’t take any precedence over the traditions of the elderly of our nation who were taught for generations and generations going back to interpret the Revival of the Dead in a literal sense. He speaks in broader terms about the significance of our traditions. In no shape or form, however, does this imply that baseless customs that have no roots in Judaism should be regarded with any significance.]
Baseless segulos and superstitions that entered our comminutes include:
Not stepping over a child for fears that it will stunt growth.[xv] Not opening an umbrella indoors for fears of it raining by your wedding.[xvi] Not allowing a baby to see itself in the mirror before it is one years old or grows its first tooth for fears of it seeing a demon in the mirror or growing up to be a bandit.[xvii] Covering the pictures and mirrors in the house of mourning.[xviii]  Not eating the end of the bread (challah). The very common custom of tying a red string around the wrist.[xix] Wearing or hanging up the Hamsa hand shape amulet.[xx] Another possible baseless custom is baking the Challah in the shape of a key (or placing a key inside).[xxi]
The superstitions recorded in Shulchan Aruch are to be kept simply out of principle because they were codified in the Code of Jewish Law—regardless of their possible origins or weak bases.
In summary, if someone were to ask me if I personally believe in segulos and superstitions, my response would be that for the most part I don’t. While many of the superstitions’ statements are true, their practical implications are slim. The effects of segulos aren’t observable and I therefore don’t regard them in my day-to-day decisions. This is to the exception of those codified in the Jewish Code of Law which we should keep as a matter of principle.
 Some attempt to explain in defense of this opinion that Saul hasn’t actually heard the voice of Saul. Instead the sorcerer herself pretended to tell over messages from Samuel. But there are two issues with this assertion. Firstly, the verse vividly says that “Samuel spoke to Saul”—without citing any mediator. Secondly, Samuel accurately predicts the death of Saul and his sons in battle the next day with the Philistines. It would be difficult to illustrate a scenario where this sorcerer would be able to predict the future. Obviously then, it was Saul himself who was indeed speaking directly to King Saul.
 Which is where the Hebrew term segula comes from. The root of the word segula means befitting, because the one practicing a particular segula becomes more “befitting” for the specific blessing or curse that the act entails.
 Because if it was black-and-white magic then there would be no atheist on planet earth who could possibly deny the observable and demonstratable supernatural act of segulos and superstitions.
 It would be hard to imagine that the sages were stupid enough to actually believe these segulos and superstitions were black-and-white. It would be equally hard to imagine that the sages believed they could fool the population into believing a black-and-white segula or superstition.
 It may be argued as well that some of the medicine wasn’t accurate even for the time and it was just the result of primitive scientific thought.
 As an example, the prohibition of eating meat and fish together due to health concerns is recorded in the Talmud and assumedly was actually a health issue at its time. However, our bodies have evolved and no such health concern exists nowadays (see Magen Avraham Orach Chaim 173). On a sidenote, we still do keep this law as a matter of principle of not diverting from what was and is practiced by world Jewry for the sake of implementing great adherence to our heritage.
 In Kabbalistic thought, the physical world is the descendant of spiritual worlds that keep on re-energizing the world anew constantly. If the nature in the spiritual worlds is to change, that would trickle down to affect this physical world. Hence, there’s a close correlation between changes in the physical human body and the way the spiritual segulos and superstitions affect us.
 It should be noted, however, that this superstition may have stemmed from Gentile cultures. See regarding luck in odd numbers—see The Anglo-American Magazine, Volume 5 page 289, also can be seen here: https://books.google.com/books?id=qDQiAQAAIAAJ&lpg=PA289&ots=wgWYnVTR8e&dq=superstition+boil+odd+number+of+eggs&pg=PA289&hl=en#v=onepage&q&f=false
 To the exclusion of those with very reliable sources; for example, those few segulos of the Lubavitcher Rebbe (e.g. learning Chitas and checking Teffilin and Mezuzos).
 And it is more reasonable to assume that the Talmud would adapt from the more dominant cultures that surrounded them than to say vise-versa.
 Except for reasons given after the “minhag” (eng. custom) becomes widespread, which obviously isn’t a convincing source.
 Notice that whenever this Rashba is quoted by the Lubavitcher Rebbe (e.g. Hisvaadiyus 5742 Vol. 1 page 276, Vol. 4 page 2124, 5744 Vol. 3 page 1430, Likutei Sichos Vol. 31 page 141, Sichos Kodesh 5729 Vol. 2 page 161, and 5736 Vol. 1 page 379) it is always regarding minhagim (eng. customs) with reasoning or meaning to them—not baseless superstitions taken from non-Jewish sources.
 Reasons were later given by various rabbis in attempt to explain this custom that has died out in the non-Jewish world but still prevails in the Jewish community. However, it is vividly clear that these incredibly vague rationalizations are only attempts to explain the customs that were already adopted from non-Jewish superstitions.
 Although this superstition wasn’t adopted from non-Jewish sources, it still has no reliable source backing it up. The apparent root of the custom probably developed from a simple Halacha that mandates to only eat the second piece cut from the challah loaf because grabbing the first cut is a sign of improper classless behavior. This later developed into a custom of not eating the ends of the bread.
 Especially if the principle of “one who is not troubled by it, will not be troubled by it” holds true regarding all superstitions.
 The principle being that we pledge full allegiance and adherence to the authoritative Shulchan Aruch so that others don’t learn to neglect the laws that they view as non-binding.
[i] Avos 2:10.
[iii] Exodus 30:13 and II Samuel Ch. 24.
[iv] See Mishneh Torah Hilchos Avodah Zara 11:16, his commentary on the Mishna Avodah Zara 4:7.
[v] E.g. Ibn Ezra and Ralbag.
[vi] These sources spoke of demons in a very tangible way: Mishna Avos 5:6, Talmud Chulin 105b, Berachos 6a, Sukkah 28a, Berachos 3b, Gittin 68b, Sanhedrin 67b, and Pesachim 100b, among many other sources.
[vii] Previous Lubavitcher Rebbe in his memoirs—http://hebrewbooks.org/pdfpager.aspx?req=15614&pgnum=199.
[ix] Shabbos 23b.
[x] Pesachim 110b.
[xi] Igros Kodesh section13 page 94 and Igros Moshe Even HaEzer 3:26.
[xii] Magen Avraham Orach Chaim 173, among other sources.
[xiii] Pesachim 110a.
[xix] https://www.thoughtco.com/the-red-thread-of-judaism-2076685—In addition to being useless, some Rabbis took issue at it from Tosefta Shabbos 7 in which the red string is listed among the prohibited Darkei Haemori (idolatrous practices).
[xxi] http://www.mesora.org/Shlissel.html. But see a vague critique to this article here: https://www.vosizneias.com/127445/2013/04/04/new-york-shlissel-challah-an-analysis/