Foetal Life

For those who keep halacha and for those who don't, few questions are as significant as the questions regarding when life begins and ends. Death is defined relatively easily as the permanent cessation of all biological functions that sustain a living organism, and although drawing the line is not always simple (e.g. regarding brain death), it is at least clear what the question is.[1]

However, when it comes to the issue of prenatal life, public discussion often gets distracted by two virtual irrelevancies. The first is the 'pro-choice' argument that women must not be told what to do with their bodies. In reality, this argument assumes that the answer to the real question is already known – the foetus has no life of its own and the only living thing being affected is the mother. By focussing on the rights of the mother (to commit potential murder), the real question is ignored.[2]

At the other extreme, the Catholic Church forbids any form of contraception or even artificial insemination, and Jewish conservatives sometimes feel the need to replicate this (perhaps so as not to be seen as 'less religious' or 'progressive'). R' Moshe Feinstein already pointed out the obvious, that these considerations have absolutely no bearing on halacha and should be cast aside.[3]

The Moral and Philosophical Perspective

Before we discuss Torah sources that may reveal when life begins according to halacha, it is important to point out the dilemma we would be in without these sources. Science may be able to tell us what an unborn baby can do at different stages of its development; it cannot define for us what constitutes sacrosanct human life. Thus for those who believe in the sanctity of human life but not in the Torah (or in any Divine revelation), it is extremely hard to justify any form of abortion.[4]

The same is true for those who do believe in the Torah, but only as an additional system that we are obligated to, unrelated to intuitive human morals.[5] As I have already written, this is not my position (see Torah and Morals). So without further ado, I shall begin to analyse the relevant sources.

Life and Soul

The Mishna tells us that if a woman is having great difficulty in giving birth, we dissect the baby inside her and remove it limb by limb, as her life takes precedence over the baby's life. However, once the majority of the baby has come out (alive) we must not harm it – we do not push away one soul for the sake of another.[6]

The clear indication is that the baby is not a 'soul' until birth,[7] and for this reason the mother's life comes first. On the other hand, even the unborn baby has independent 'life' that is only superseded by the life of the mother (which also contains a soul).

Another Mishna tells us that if a pregnant woman is sentenced to death for her own crime, we do not wait for the baby to be born before carrying out her punishment. The gemara derives this halacha from a pasuk, but first states that in fact it would have been obvious as the baby is part of the body of the mother. The only reason that the Mishna needed to record this halacha, and that the pasuk is required, is because otherwise we could have argued that it would be not be fair to deprive the father of his rights to the baby.[8]

Why was it at first obvious to the gemara that the life of the unborn baby is not important enough to justify delaying the mother's execution? The wording of the gemara's question would seem to imply that the baby is simply part of the body of the mother and therefore included in the death sentence. So does the baby have independent life or not?

I believe that the answer is simple, and can be found within the Mishna itself. The Mishna continues that if the sentenced lady has already 'sat on the birthing stool', we do wait for her to give birth. It appears that only at this point does the baby have independent life. Thus, the gemara quoted above only needed to explain that the mother's life supersedes the baby's because birth was already imminent. At an earlier stage, the unborn baby is simply a part of the body of the mother and the permissibility of its dissection in order to save the mother is obvious.[9]

Thus, we have three different halachic stages in the development of a baby. For most of pregnancy, the baby does not have its own life at all. Life begins when the baby is about to be born, and the 'soul' only enters the baby at birth. We now need to investigate some of the halachos that may or may not be dependent on these three stages. It should go without saying that due to the severity of the issues involved and the need for assessment on a case-by-case basis, the following should not be taken as a definitive ruling.

Shabbos

Are the laws of Shabbos deferred in order to save the 'life' of an unborn baby? It may surprise some readers to know that the answer is not straightforward,[10] and that while Behag ruled in favour of saving the unborn baby,[11] the Ramban quotes those who disagree.[12]

The first gemara quoted above continues by saying that if the mother dies during childbirth, if necessary we carry a knife through the reshus harabim in order to cut open the mother's dead body in an attempt to save the baby.[13] The Ramban cites this gemara in support of the view of Behag, but points out that there is in fact no conclusive proof from here. Once the mother has died and is no longer sustaining the baby, her body is no more than a door behind which the baby is locked. If the baby is still alive, it has already been born.

Elsewhere, the Ramban assumes that the Behag is correct but asks what the justification is for the laws of Shabbos being relaxed for the sake of being which is not a 'soul'? He answers based on the dictum "Transgress one Shabbos for him, so that he will keep many Shabbosos."[14] As such, Shabbos can be broken irrespective of the current status of the baby.[15]

Murder and Abortion

The Torah tells us that one who strikes a pregnant woman, causing a miscarriage, must pay damages. Capital punishment is not exacted.[16] This is perhaps the clear source in the written Torah for Chazal's understanding that an unborn baby does not have a soul.

However, the gemara derives that a non-Jew is liable to the death penalty for even this level of bloodshed.[17] Although there may technically be no soul (or even life), it is quite clear that performing an abortion is in general a severe transgression. The gemara compares even masturbation to murder,[18] despite the fact that there is clearly no life involved. Intentional misuse of one's reproductive organs contains an element of contempt for human life, even when no-one is harmed by it.[19]

Furthermore, even if abortion is not murder and the foetus is just a part of the mother, it is certainly forbidden for a person to destroy or even to injure a part of his or her body.[20]

Extraordinary Circumstances

All of the above shows clearly that abortion is certainly forbidden under normal circumstances. Of course, no sane woman intentionally becomes pregnant in order to abort, so when the question arises, the circumstances tend not to be normal. In each case, it will be necessary to examine whether there can be any dispensation regarding the problems that we have raised.

The question of self-harm will rarely be an issue. Surgery is permitted in order to prevent pain,[21] and this includes psychological pain.[22] However, we must point out that abortion is not just self-harm, as the father also has a stake in the baby. Any leniencies will be dependent on the consent of the father to performing the abortion.[23]

Even with the consent of the father, there can be no justification for terminating a pregnancy if we may even do melacha on Shabbos to save the baby. Unless we are willing to reconsider the accepted ruling regarding Shabbos, to my mind the only circumstances under which abortion may be permitted (if the mother is not in danger) are when the baby is known to be deformed to the extent that it will never be able to keep mitzvos. Here, the logic of the Ramban does not apply and we would not allow the unborn baby to be saved on Shabbos.[24]

May we all be blessed with healthy children and further generations!

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[1] See https://en.wikipedia.org/wiki/Death#Problems_of_definition

[2] Some have argued that even were the foetus to be an independent living entity, the mother should not be forced to preserve it using her own body. Were a person to be forcibly used as a dialysis machine for another, thus saving the other person's life, it would not be unethical to disconnect oneself and thus cause the other's death (see this Wikipedia article).

However, this argument is problematic for two reasons. Firstly, the claim regarding the 'human dialysis machine' is itself incorrect. Detaching oneself in such a situation would be murder, and there simply is no justification for murder unless one's life is being endangered by the other person. Secondly, even were there to be such justification, this certainly would not extend to a case where a person himself was responsible both for another's need for dialysis, and for becoming attached to this person in the first place. Only a case of rape would be comparable to the case of the person forcibly used for dialysis.

[3] Igros Moshe, Even Ha'ezer 2:11. While many within the Catholic Church also forbid abortions even in order to save the life of the mother (see Wikipedia), thank G-d no Jewish authority has followed suit on this issue as the mishna explicitly permits (and obligates) such action.

[4] Of course for these people it is also hard to see why human life would be especially sacrosanct (i.e. inherently more important than animal life). Those who follow atheism to its logical conclusion have indeed posited that there is no inherent difference between humans and animals, and have legitimised infanticide in some circumstances (see https://en.wikipedia.org/wiki/Peter_Singer#Abortion,_euthanasia,_and_infanticide).

[5] See https://mikyab.net/posts/3688 (in Hebrew).

[6] Ohalos 7:6

[7] See Rashi to Sanhedrin 72b who writes this explicitly in explanation of this halacha.

[8] Arachin 7a.

[9] See also the Ran's commentary to the Rif, Chulin 19a, who writes in a matter of fact way regarding the sentenced woman "we are not concerned about the baby" at this stage.

[10] The sources discussing the symptoms which permit a pregnant woman to eat on Yom Kippur (see Mishna Yoma 82a and the gemara thereon) are not conclusive, as the concern maybe the safety of the mother and not just of the unborn child.

[11] Siman 7, Hilchos Shabbos chapter 18.

[12] Toras HaAdam, Sha'ar HaMeichush, Inyan HaSakana. Interestingly, the Noda Biyehuda writes that we can break Shabbos to save the baby only if the woman is about to give birth, the distinction that we made above regarding life (Mahadura Tinyana, Choshen Mishpat siman 59. See also Chidushei R' Chaim Halevi, Hilchos Rotzeach).

[13] Arachin 7a-b.

[14] Chidushei HaRamban, Niddah 44b.

[15] This explains why according to Behag, melacha can be done on Shabbos even for the sake of a foetus that is not just about to be born. This is also the generally accepted halacha nowadays (see for example Shemiras Shabbos Kehilchasa 36:2). However, I would question how far the dictum of breaking Shabbos for the sake of future Shabbosos can be taken. Some have already ruled that Shabbos can be transgressed even to save fertilised eggs in a lab freezer (see this responsum). Extrapolating further, one could argue that fertility treatment could also be permitted on Shabbos.

[16] Shemos 21:22-3.

[17] Sanhedrin 57b. Non-Jews are liable to the death penalty for even lesser crimes such as theft and eating a limb torn from a living animal. However, in this instance, the crime they are killed for is murder. Some see this as an indication that killing a foetus is considered murder for Jew and non-Jew alike (see Igros Moshe, Choshen Mishpat 2:69), but this is far from conclusive.

[18] Nida 13a

[19] The Chavas Ya'ir (siman 31) indeed writes that abortion is forbidden as a form of 'destroying seed.' This is far from obvious, as this prohibition is directed at the manner in which the seed is extracted from the body rather than what is done with it after it has left the body (the destruction of laboratory sperm is not included). However, abortion is clearly a more severe version of the element of contempt for human life involved in masturbation.

[20] Mishna, Bava Kama 90b.

[21] Shabbos 50b

[22] Tosfos there (ד"ה בשביל צערו). Some authorities even allow surgery for aesthetic purposes alone (see Igros Moshe, Choshen Mishpat 2:66), but this is far from conclusive (my own writing on this topic in Hebrew is available on request).

[23] It is only here that there is an understandable conflict between the Torah and the 'pro-choice' / feminist movement. The Torah's position is however unambiguous – until birth, the father has ownership of the foetus even if he is not married to the mother (Bava Kama 43a). Only the product of an incestuous or adulterous relationship may not be owned by the father according to some views (see Yerushalmi quoted by Tosfos there; Minchas Chinuch 49; Techumin volume 9 page 57).

[24] This of itself is not proof that abortion would be permitted, as the life of such a baby also has a value (albeit not one significant enough to permit melacha on Shabbos prior to birth). My inclination is that parents would not be obligated to continue such a pregnancy, but this is subjective. 

Free Will & Hashem's Omniscience

Introduction

One of the oldest philosophical questions within Judaism (and outside of it) is the possible contradiction between Hashem's Omniscience (knowledge of all) and our own free will. The question was perhaps made famous by the Rambam, but was already recorded many years previously.

The apparent contradiction is that if Hashem knows everything, including future events, a human (or any other creation) cannot possibly choose to act differently to the way Hashem knows he will act. Thus, even though a person is unaware of what he himself will decide in the future, he cannot be said to be acting out of free will.

Whenever there are two seemingly contradicting principles, there can only be three options:

1)      The contradiction can be resolved.
2)      The first principle is wrong.
3)      The second principle is wrong.

It may come as a surprise to many, but to some extent, all three possibilities have their advocates among the rishonim. We will start by analysing the first option, which is perhaps the most commonly accepted and the position of the oldest Jewish written works.

Is there even a problem?

Although many do believe that this contradiction can be resolved, there is considerable variance within this school of thought as to how easy the resolution is. R' Sa'adia Ga'on (10^th century, Egypt/ Eretz Yisrael / Baghdad) dismisses the whole issue as a non-question – although Hashem knows what a person will do, this knowledge is not the cause of the person's choice. On the contrary, the person's choice affects Hashem's knowledge in the past.[1]

What was obvious to R' Sa'adia was far from obvious to others. The idea that the future can affect the past (Retrocausality) is a topic debated by philosophers and is not limited to theological discussions.[2] It is also worth noting that R' Sa'adia's argument is not dependent on any Divine qualities that are beyond our understanding – according to his logic, there would also be no inherent problem in a human foreseeing a free will choice made by another human with 100% accuracy.[3]

By contrast, R' Bachaye ibn Pekuda (11^th century, Spain) writes that were we able to understand the resolution of this contradiction, Hashem would have revealed it to us.[4] In other words, although there is a resolution, we are incapable of understanding it.

This view is echoed by the Rambam, although he adds more of an explanation as to why we are incapable of understanding. While humans have characteristics that are separable from their essence, Hashem does not. No positive characteristics can be attributed to Hashem – He and 'His knowledge' are One. As this is a concept that us humans cannot fully fathom, we are also incapable of understanding how Hashem attains knowledge of human choices. The only thing we can be assured of is that we do indeed have free will.[5]

The problem with this is that even after we accept that Hashem's capability of seeing the future is not something we can understand, we are left with a contradiction from the human point of view. Unless we accept the retrocausality of R' Sa'adia Ga'on,[6] Hashem's unerring knowledge of the future means that there is no possibility that we will in fact decide something different.

It would therefore appear that when the Rambam insists that we have free will, this only means that our decisions are made willingly. We do not actually have any real option to do something different to that which Hashem knows we will do.[7] This is notwithstanding the fact that the Rambam spends this entire chapter stressing that free will is a fundamental principle of the Torah[8] and that those who deny it are foolish.

If this understanding of the Rambam is correct, we can better understand the criticism of the Ra'avad of his words. The Ra'avad writes that a wise person should not raise difficult questions without resolving them, lest this causes any heretical thoughts in the mind of the reader. This criticism is more understandable if the Rambam himself could have helped us by clarifying that free will is more limited than we may have thought.[9]

'Inability' to do the impossible

We now move on to the second option above. Suggesting any limits to Hashem's knowledge may seem heretical, but this is based on a lack of both knowledge and understanding. Nowhere do Chazal state in an unequivocal manner that Hashem foresees all future events (although it is quite clear from Tanach that He does foresee many of them).[10]

The Rambam's himself, while listing Hashem's Omniscience as the tenth principle of faith, does not mention the future. His statement of Hashem's knowledge of all future events only appears in the context of his discussion of free will. It appears that the Rambam derived this concept from the general principle that Hashem is perfect and is lacking nothing.

However, as the Rambam writes elsewhere, it does not make sense to describe Hashem as able to do the logically impossible, such as creating another entity like Him.[11] It follows that if knowledge of our future decisions is a direct contradiction to our free will, Hashem's 'lack of ability' to create such a contradiction would not reflect any real lack. He simply chose to grant us free will, thus 'forgoing' His own prior knowledge of what we would choose.

This is the position of Ralbag (1288-1344, Southern France).[12] The Rambam could not follow this line of logic, as his view is that time itself is merely a creation of Hashem.[13] The idea that Hashem's own creation could limit Him is itself a contradiction.

One thing should be clear. As the view of the Ralbag does not attribute any lack of perfection to Hashem, and the dispute revolves around the philosophical understanding of the concept of time – this view is well within the acceptable limits of Jewish religious belief.[14]

Determinism

Perhaps even more surprisingly, R' Chisdai Kreskas goes to the opposite extreme. Preferring to accept the position that Hashem does foresee all future events, as well as due to other philosophical arguments, he concludes that human actions are always just the net results of all the natural causes acting on a person (both from within the person's nature and from external sources). Although we do not feel anything forcing us to act in a certain way, the reality is that we have no choice.

This leads to the obvious question as to the justification of reward and punishment for our actions, which are not in our control.[15] R' Chisdai is clearly aware of the problem and writes at great length to attempt to resolve this. He first claims that reward and punishment are necessary tools with which to influence our decisions for the good (these are some of the many factors that force us to act in the way we do), and this end justifies even the punishment of the innocent.

However, he goes on to ask that if this is the case, why can't there be punishment even for those who act entirely under noticeable duress? His conclusion is that in fact reward and punishment is not for the actions themselves that a person carries out, rather for the frame of mind in which they act. One who happily serves Hashem earns reward for his joy, and the same is true for the converse.

With this, R' Chisdai Kreskas concedes that regarding our feelings, we do in fact have free will. Although he does not revisit the question of Hashem's prior knowledge of everything, the clear implication is that Hashem can only foresee what our actions will be, not our mental attitude towards them. Thus this view actually combines both the second and third options, limiting both Hashem's knowledge of the future and our free will!

On a philosophical level, it is hard to see what is gained by this strange combination. Nevertheless, as R' Chisdai Kreskas does not deny the concept of reward and punishment or the justness of the ways of Hashem, this view also certainly remains within the limits of legitimacy.

May we use our free will (whatever level we have) for the good, and on Yom Kippur attain forgiveness for any bad decisions we may have made in the past!

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[1] Emunos v'Deyos, Ma'amar 4.

[2] One of the main arguments against the possibility of retrocausality is that were it possible to have an effect on the past, this would lead to time paradoxes. On the other hand, retrocausality is observed within quantum mechanics. Therefore, R' Michael Avraham argues that retrocausality is only possible within deterministic processes and not cannot be affected by decisions made with free will.

[3] Of course, humans cannot do anything with 100% accuracy. However, this is due to human qualitative deficiency, rather than any logical impossibility.

[4] Chovos Halvavos, Sha'ar 3 (Sha'ar Avodas HaElokim), chapter 8.

[5] Hilchos Teshuva 5:5

[6] The Rambam appears not to – otherwise the question would not require an answer unfathomable to us.

[7] Thus the Rambam is not as strong an adherent to option 1 above – his position is somewhere between option 1 and option 3.

[8] R' Nahum Rabinovitch calls this the 'fourteenth principle of faith' of the Rambam (Mesilot Bilvavam, p.54).

[9] I understand the answer that the Ra'avad suggests, that Hashem knows 'like the knowledge of astrologers, who know through an external power how another will act', as being equivalent to my understanding of the Rambam. The Ra'avad's conclusion, that this answer is not enough, is presumably because of a reluctance to accept that free will is limited in this way.

[10] The Rambam understands that a statement to this effect, together with the principle of free will, appears in the Mishna in Pirkei Avos (3:15). However, this explanation is not obvious from the context of the Mishna, and neither is it unanimously agreed upon (see for example Bartenura for an alternative explanation).

[11] Moreh Nevuchim 3:15

[12] Milchamos Hashem, Ma'amar 3, Chapter 4. This was also later the position of the Or HaChayim (Bereishis 6:5) and the Sh'lah (in his introduction).

[13] Moreh Nevuchim 2:13. It is however unclear how the Rambam knew that time was a creation.

[14] See The Limits of Legitimate Belief, where we supported the view of the Ra'avad, that the same is true even regarding the mistaken view that Hashem has a physical form.

[15] Or Hashem, Ma'amar 2, Klal 5.

Carrying on Shabbos Part 2 - Entrances or Imaginary Walls?

Rabbinic Prohibitions

Our discussion in Part 1 focussed almost entirely on the definition of the reshus harabim (public domain), in which carrying is Biblically forbidden on Shabbos. Other than negating the status of a reshus harabim by building gates at the ends, there is no way to make carrying in or through the reshus harabim permissible.[1]

Carrying in or between areas which are not reshuyos harabim is permitted on a Biblical level. However, Chazal forbade carrying in many of these areas out of concern that either the physical or the conceptual boundaries of the reshus harabim could easily become blurred. Broadly speaking, these rabbinic prohibitions fall into four categories:

1. Areas that are open enough to resemble a reshus harabim were given the name 'Carmelis,' an area that is neither a reshus harabim nor a reshus hayachid (literally private domain).[2] Carrying in these areas, between them and a reshus hayachid or between them and a reshus harabim, is forbidden rabbinically until they are suitably enclosed.
2. In some areas that are sufficiently enclosed to have the halachic status of a reshus hayachid, it is nevertheless rabbinically forbidden to carry due to the proximity to the reshus harabim and the concern that one may not notice where the reshus harabim starts. Depending on the situation, these prohibitions may be obviated by erecting a marker post (lechi) or crossbeam (korah) at the exit to the reshus harabim, as a sign to remind people not to carry any further.[3]
3. In areas that are not intended for human habitation, such as crop fields or industrial areas (known as karpifos), even if fully enclosed, it is forbidden to carry unless the area is no larger than 5,000 square amos (roughly 1,100 m²).
4. Due to the conceptual similarity to the reshus harabim, Shlomo HaMelech instituted that in order to carry in areas that more than one person or household have right of access to, an 'eruv' (known as eruvei chatzeros) is required.[4] A loaf of bread[5] is transferred to the joint ownership of all of those with access to the common area, thereby uniting everyone as if they all lived in the place where the food is kept. 

Practically speaking, nowadays the second category of restrictions is usually subsumed within the first. Due to complications as to when a lechi or korah may be sufficient to permit carrying, we require the more significant marker of a tzuras hapesach, consisting of two posts and a crossbeam or crosswire on top of them.[6] The tzuras hapesach serves the dual purpose of both completing a halachic enclosure (as will be explained shortly) and acting as a boundary marker.

Our discussion here will therefore focus on the remaining points above, starting with point 1.

Halachic Enclosures

We first need to establish what is considered halachically 'enclosed.' The rishonim dispute how many of the four sides must be walled in order for an area to count as a reshus hayachid – the Rambam requires all four whereas the Ra'avad argues that three are sufficient. However, this dispute is not relevant to our discussion, as the Ra'avad agrees that on a rabbinic level, walls are required on all sides in order to permit carrying.[7]

This does not mean that solid walls are required for the entire length of all four sides. Small gaps, with a width of less than three tefachim (around 23cm), are considered 'filled.' Larger gaps are also permitted, as long as 1) they do not form the majority of any side, and 2) each gap is of less than ten amos (around 4.6m), and as such can be viewed as an 'entrance.'[8]

We have also already seen that where there are already walls on three sides, the fourth side requires only a tzuras hapesach. The Mishna tells us that this is sufficient even if the entrance is more than ten amos wide,[9] and this is the accepted halacha despite a dissenting opinion in the gemara.[10]

The simple explanation for this is that as the tzuras hapesach creates a clearer appearance of an entrance, the gap does not invalidate the enclosed nature of the area despite being wider than an ordinary entrance. This will also explain another halacha of the tzuras hapesach – it must be strong enough to hold a simple straw door. According to one opinion in the gemara (not commonly accepted as halacha), there must also be hinges.[11]

Walls Out Of Nothing?

With the above in mind, it is surprising that the gemara also tells us that the Chachamim approved of an innovative solution to the problem of Kilayei Zeraim (mixed sowing) implemented by a person from the valley of Beis Chursan. He put up four posts in the four corners of a field and stretched a branch on top of them, thereby 'enclosing' the area and allowing it to be sown with a different crop than the one in the surrounding area.[12]

From this gemara it would seem that a tzuras hapesach can function not just as an 'entrance' – it can make up an entire wall, even if all four 'walls' are mere 'entrances.' This is a major extension to the more intuitive use of a tzuras hapesach. Furthermore, the gemara proceeds by equating to Hilchos Shabbos.[13] How does this fit in with our understanding above?

There are (at least) three basic approaches within the Rishonim:

Tosfos – Tzuros Hapesach really can act as complete 'walls', even on all four sides. According to this view, any area without a reshus harabim can become halachically 'enclosed' as if by magic, using poles and wires alone (i.e. the 'entrance' approach described above is not correct).

Ritva – The comparison to the laws of Kilayim is not in fact a full comparison. Regarding Kilayim there is no need for an enclosure, as only one 'wall' is required to separate between two types of crop. Although in the case in the gemara it happened to be that the crops in the middle were surrounded by different crops and required tzuros hapesach on all sides, these four tzuros hapesach worked independently from each other. Regarding Hilchos Shabbos, it certainly would not be possible to 'enclose' an area using poles and wires alone.

Rambam – Concerning Kilayim, the halacha is not in accordance with the ruling of the Chachamim in the case above, and a tzuras hapesach is not a valid way to separate between two types of crop.[14] As far as Hilchos Shabbos is concerned, tzuros hapesach can only be used if the majority of the circumference of the enclosure consists of real walls.[15]

The majority of large scale Eruvin rely on poles and wires for most of the circumference of the 'enclosed' area, based on the view of Tosfos.[16] While it is unusual to hear of objections to Eruvin for this reason, the reality is that this leniency is far from insignificant.

Other Issues

We are now ready to move on to the remaining categories of related Rabbinic prohibitions. I do not have much to write about the third category above, relating to areas not designed for human habitation.[17] It is just important to bear in mind that any such areas within an 'Eruv' will need to be enclosed independently, in order to separate them from the areas in which carrying may be permitted. 

The final issue that does require some clarification is the eruv itself (note that the 'eruv' is the food used to join everyone together, not the poles and wires). While making this eruv is not hard, two difficulties often arise.

Non-Jews, or those who 'do not believe in the eruv' (i.e. those who are not religious), cannot be included in the eruv and as such, their presence may forbid everyone else from carrying. These people need to be symbolically 'bought out' by paying them a minimal amount for their rights of use of the communal areas (this does not affect their actual rights of use, and is purely symbolic).[18]

In most big cities, it would clearly be impractical to make these 'purchases' from all such individuals. Instead, we rely on a leniency given by the gemara, allowing the purchase to be made from anyone who has access to the person's property, including any workers that he may employ.[19]

By extension, it is common practice to 'purchase' the rights of all non-Jews and non-observant Jews from a centralised authority, who has the rights to enter all private property in an emergency. This may be the police, the fire brigade, or even the government.[20] However, in democratic countries nowadays it is not so clear that the more limited power held by these institutions is sufficient. As a minimum, it is imperative to ensure that the 'purchase' is made from an authority that holds at least this minimal power.[21]

Conclusion

These two posts are far from a comprehensive explanation of all the laws of carrying on Shabbos, or even of all the laws commonly relevant. I hope however that I have provided a rough outline, and increased appreciation of the complexities of some of the issues. As always, any questions or challenges are welcome.

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[1] See Eruvin 6a-b, commentaries thereon and Shulchan Aruch Orach Chaim 364:2. As this is not a practical option in almost any city in the world, I will not elaborate on the requirements. I will simply say that even according to the view of the Rambam, that these gates need not be locked each night (Hilchos Shabbos 17:10), I believe that they do have to have the real appearance of gates, and not something hidden away that has no possible non-halachic function.

[2] See Rambam, Commentary to Mishna Shabbos 1:1 regarding the etymology of this name.

[3] The function of the lechi and korah is subject to a dispute in the gemara (Eruvin 11b-12a) and rishonim which requires extensive analysis. However, according to the overwhelming majority of views, a minimum requirement of these markers is to act as a distinctive sign as described above.

[4] Eruvin 21b.

[5] In order to join several alleyways together (shituf mevo'os), other food items can be used.

[6] See Shulchan Aruch and Rema, Orach Chaim 363:26

[7] Hilchos Shabbos 17:9. The practical ramification to the dispute is regarding one who carries from the reshus harabim to an area enclosed on three sides (or vice versa). According to the Ra'avad, this is a Biblical violation and a sin-offering is required for atonement – the need for a fourth wall is only rabbinic. The Rambam, on the other hand, maintains that an area with only three walls is never a Biblical reshus hayachid. According to him, an alleyway with just a korah (crossbeam) at the end is a special case where Chazal allowed carrying in an area that is not a Biblical reshus hayachid.

[8] Mishna, Eruvin 15b.

[9] Eruvin 2a.

[10] See Eruvin 11a (also see Rosh and Hagahos Asheri there), Shulchan Aruch Orach Chaim 363:26.

[11] Eruvin 11b, Shulchan Aruch Orach Chaim 362:11.

[12] Eruvin 11a.

[13] Although there is a dispute to what extent the laws of Kilayim and the laws of Shabbos are equivalent, the conclusion of the gemara is that this dispute is regarding a technicality. The basic halacha appears to apply equally to Shabbos.

[14] In Hilchos Kilayim, chapters 3-4, the Rambam discusses various ways of separating between different crops, never mentioning the idea of a tzuras hapesach or anything similar (there must be a physical separation, either a land feature or a certain distance). Presumably, the Rambam understood from the omission of this solution in Mishnayos in Kilayim and other related gemaros, that the consensus of Chazal was against the lone gemara quoted above.

[15] Hilchos Shabbos 16:16. See Magid Mishne there, who raises a possibility that the Rambam may agree that tzuros hapesach of less than ten amos width may be used even for the majority of the circumference, similar to his position in Hilchos Sukka (4:12). However, in the words of the Rambam in Hilchos Shabbos there is no hint even to this leniency.

[16] The Shulchan Aruch appears to understand that this is the majority opinion, and also assumes the lenient understanding of the view of the Rambam suggested by the Magid Mishne above (Orach Chaim 362:10).

[17] There are disputes regarding what constitutes a 'karpaf' that cannot be included in an eruv, but much of this is subjective and it is hard to write about it in general terms.

[18] This requirement was made as a means of dissuading people from allowing non-Jews, who were historically often an antagonistic presence, to reside in Jewish areas. See Eruvin 61b-62a.

[19] Eruvin 64a.

[20] See Shulchan Aruch, Orach Chaim 391:1.

[21] The problem may be exacerbated by home movers (in Israel it is not at all unusual for irreligious Jews to move on Shabbos). Although in general the halacha is that once a kosher eruv is made, new arrivals do not create a problem (see Eruvin 89b and 93b), there are several exceptions to this (see Chazon Ish, Orach Chaim 88:2 for a summary). However, it would seem logical to say that if the 'purchase' from the relevant authority was valid, it should be effective with respect to the new residents as well.