From Ramchals "The Way of G-d":
http://www.torah.org/learning/ramchal/classes/class32.html
"The Way of G-d"
Part 1: "The Fundamental Principles of Reality"
Ch. 5: "The Spiritual Realm"Paragraph 1
We're about to begin a rather long foray into the "backdrop" behind everything we know (and don't know)-- the spiritual realm. Let's remember from the outset, though, that we've already discussed G-d, who can be said to be the "backdrop *behind* the backdrop", if you will. So what we'll be focusing upon now are the various "paraphernalia" and "tools" G-d has set up and uses.
Ramchal starts off with a rather simple lay-out of a dualistic universe, indicating that there are *physical* things and *spiritual* things. Both realms have their own "laws" and fulfill their own objectives. (Note to those who'd argue that the world only appears to be dualistic, and that it's really a combination of material and spiritual: We'll soon see that only human beings are a true combination of material and spiritual.)
He then offers us some definitions.
Physical phenomena are things we can experience with our five senses (or with devices that expand on them), regardless of how vast or minute, blunt or subtle, they may be. They’re either close at hand, here on earth; or far off in the heavens.
Spiritual phenomena are things we can't experience with our five senses (nor by means of any devices), and they too are either "close at hand" (which is to say, they're either *souls* that connect to physical bodies); or they're "far off in the heavens" (or they’re *transcendent entities* that don't connect to physical bodies).
There are two types of transcendent entities: *forces* or *angels*. We'll explain forces later on in the course of this chapter. Angels are immaterial, celestial agents of change, rather than the sort of "fairies", "winged spirits", or the like they're often taken to be.
There's actually also a *third* sort of phenomenon that's neither specifically spiritual or physical but acts as an intermediary between the two, known as "sheidim" in Hebrew. That term is usually translated as "demons", which has a decidedly sinister ring to it. "Phantoms" or "ghosts" are closer to the sense of the word; but those terms also carry certain connotations that are off the mark.
Suffice it to say that "sheidim" are phenomena that can't be experienced with the five senses, so they might be thought to be spiritual; yet they interface with the material world, so they might be thought to be physical. But they're actually of a class all their own, and are neither spiritual nor physical. It's pointed out in the Talmud that sheidim are all around us all the time. They’re more numerous than we, and we'd in fact be thunderstruck and undone if we were actually able to see them (Tractate Berachos 6A).And then there’s humankind. We are the only entities that are comprised of both a spiritual soul and a physical body. While other, lesser beings like animals *do* have a soul, it would be more accurate to characterize their "souls" as "energy fields" rather than actual souls. For while those energy fields are truly the most ethereal of all physical phenomena, they're nonetheless not spiritual.
Our human souls are utterly transcendent, and they don't express themselves in the course of our day-to-day experiences. For, again, they’re non-physical and hence can't be detected by any of our five senses. Hence when people speak of "being in touch with their souls" they mean to say that they're in touch with their deepest feelings, aspirations, or convictions. For the soul simply can't be experienced through the senses (or the heart-- since the things we sense in our hearts are rooted on a very deep and subtle level in the sense of touch).
http://www.ou.org/torah/tt/5767/nitzvay67/navi.htmhttp://www.shemayisrael.co.il/dafyomi2/pesachim/insites/ps-dt-109.htm
109b
2) "ZUGOS" AND "SHEIDIM"
The Gemara discusses at length the concern of performing certain actions in pairs (such as eating or drinking a multiple of two of any item), and how doing so gives certain power to the Sheidim to do harm. What is the understanding behind the Gemara's concern for Zugos, and do the Gemara's statements apply to us, nowadays?
[1] WHY "ZUGOS?"
The Acharonim propose different rationalizations for the phenomenon of "Zugos," or pairs?
(a) The SEFER MALKIEL teaches that the existence of Sheidim represents the forces of nature through which Hashem punishes those who demonstrate a lack of faith in Hashem. The primary description of Hashem that we know is that Hashem is One. He is the ultimate and only One, the pure Singularity in the world. When a person performs an act of Zugos, or "multiplicity," he gives the Sheidim a foothold by demonstrating a lack of Oneness in the world. When a person eats an odd number, such as three, then the even numbers pair and cancel each other out leaving a singular "one," and that is why the Sheidim have no power over odd numbers.
(b) The MAHARAL (Gevuros Hashem, ch. 38; Be'er ha'Golah, Be'er ha'Sheni, p. 28; Nesivos Olam, end of Nesiv ha'Avodah) adds a reason to explain *why* the Sheidim dominate wherever there is a lack of Yichud Hashem.
The Maharal explains that the Sheidim are a secondary consequence of the Creation of the world. That is, when Hashem created the world, a secondary outgrowth was the development of Sheidim. That is, they were not meant to be the purpose of Creation, like the other creatures of the world. Rather, they are a consequence of Creation, and they came into being since the world would not be complete without them. Since their whole existence is secondary, i.e. with a less direct connection to Hashem, they have power over anything that is secondary, i.e. which is less directly connected to Hashem.
(c) Following the path of the Rambam, who, in Moreh Nevuchim, rationalizes most Mitzvos that seemingly lack purpose by connecting them to the practice of early idolators, the following may be suggested. One of the basic tenets of the belief of the polytheists, who believed that there were many gods, was that all of the gods stemmed from two basic forces, one of good and one of bad (Sanhedrin 39a). Therefore, they had a practice to make sure to eat two of everything to satisfy the forces of both good and evil. For this reason, the Rabanan decreed that the Jews should be careful not to eat two of everything, and certainly not to do so intentionally, for doing so demonstrates a trace of idolatry for which a person will be punished. (M. Kornfeld)
[II] "ZUGOS" TODAY
What is the Halachah? Do the stringencies of Zugos apply today?
(a) The RASHBAM (110a, DH Rabah) writes that as time went on, the concern for Zugos decreased more and more. (According to the third explanation above this is very logical, because no one remembers nowadays how the idolaters used to conduct themselves.) We find that even in the times of the Amora'im, the concern for Zugos was decreasing, as the Rashbam explains.
TOSFOS (Yoma 77b and Chulin 107b) explains that nowadays (that is, during the times of Tosfos), we no longer show any concern for Zugos at all. Apparently, he explains, the forces that had power over Zugos have become so diminished that they are extremely rare and do not warrant any concern.
However, the TUR (OC 170) briefly writes that one should not eat or drink anything in pairs. He also mentions (OC 183) that a person should not recite Birkas ha'Mazon after drinking two cups of wine during the meal, because he will be so worried about Sheidim harming him that he will not be able to concentrate on the blessings. The BEIS YOSEF there writes that the Tur should have omitted this Halachah, because Tosfos writes that the Sheidim are no longer prevalent, and in the SHULCHAN ARUCH he indeed leaves them out. The Acharonim suggest various answers as to why the Tur mentions Zugos at all.
Perhaps the TUR mentions the Halachah of Zugos with regard to Birkas ha'Mazon because in the case of Birkas ha'Mazon, it is a matter of one's ability to concentrate on the blessings. A person might not be able to concentrate if he drank two cups during the meal, because he is so worried about being harmed by Sheidim. Even though, in reality, there is no longer any concern for Sheidim, some people are still worried about them, and such a person's mind will not be clear and calm enough to concentrate when he recites Birkas ha'Mazon. Therefore, the Tur says that he should not recite Birkas ha'Mazon after drinking two cups.
Why, though, does the Tur mention that a person should avoid eating or drinking in pairs? It could be that even though right now the Sheidim are no longer prevalent, and in everday practice we do not have to be concerned with eating Zugos, nevertheless, the Tur means to caution that we should never enact a decree or create a custom that involves eating or doing something in pairs. The reason for this is twofold. First of all, perhaps the Sheidim will return. Furthermore, the Gemara (110b) says that even when the Sheidim have no power, "Kishuf," witchcraft, still has power over Zugos. That is, if a sorceror sees someone eating Zugos, he can harm him more easily. Although, we are normally not concerned with the possibility of "Kishuf," since it is rather rare to meet up with a sorceror, nevertheless, a decree or custom that will put a person in danger of Kishuf should be avoided.
QUESTION: We might ask, how could the Rabanan make an enactment to eat Lechem Mishnah -- two loaves -- on Shabbos? That should be a problem of Zugos just like drinking the Arba Kosos!
ANSWERS:
(a) When it comes to the Arba Kosos, the Rabanan decreed that one must drink the entire cup (and by drinking a majority of the cup, one is considered as if he had consumed the entire cup). In contrast, when it comes to Lechem Mishnah, there is no requirement to eat two *entire* loaves of bread. Just reciting ha'Motzi over Lechem Mishnah is not considered Zugos. (Y. Shaw)
(b) Our Gemara (110b) says that loaves of bread does not have a problem of Zugos because they are "completed in the hands of man." (However, some old texts of the Gemara, as well as that of Rabeinu Chananel, do not have the Girsa there of "Kikaros.")
(c) The MAHARSHAM cites the Zohar (Parashat Ekev, p. 273a) that asks this question and answers that Sheidim do not have dominion on Shabbos (although they apparently *do* have dominion on Yom Tov, as we see from the Gemara's question concerning the Arba Kosos). RAV YAKOV EMDEN asks that our Gemara (112b) concludes that the Sheidim are *more* prevalent on Friday night than during the week! In fact, this is why we do not recite the verses normally recited before Shemoneh Esreh (in Chutz l'Aretz) on Friday night; so that we will finish Ma'ariv late and have to return home after dark, and after the lamps have gone out (TUR OC 267, citing the Ge'onim).
How is this to be reconciled with the Zohar, which says that the Sheidim have no power on Shabbos? Furthermore, He answers that the Zohar itself asks this question (Vayakhel 205a). The Zohar answers that the Rabim (public) have nothing to fear on Shabbos. Individuals, though, could be affected by the forces of the Sheidim on Shabbos. Since Lechem Mishnah was enacted for everyone, there is no concern for Sheidim. An individual, though, should not go out alone on Friday night, out of concern for the Sheidim that dominate then.