"An eye for an eye" is arguably the most misunderstood Jewish commandment. Most condemn it as too harsh, some praise it as just, but few cared to actually read it. This commandment applies to the narrow class of situations only rather than to all crimes.
It is indeed odd to imagine that ancient Hebrews diligently pulled out a tooth of someone who kicked out a tooth. Realizing the impracticality of such strictly defined reciprocity, sages reinterpreted it as monetary compensation: a tooth' value for a tooth kicked out. That, too, ran into practical difficulties: what is a tooth's value? Obviously, the value of the last tooth is greater than of the 32nd tooth. A lost tooth doesn't diminish one's "reference value" at slave market. A bruise, which is temporary, doesn't affect one's permanent value at all, and so the sages declared a bruise value to be a price someone would ask to willingly suffer such bruise. That definition, too, is unworkable, as a rich man and a poor one would value the bruise widely differently, thus defying the common legal guidelines. Besides all of that, there is no hint in the Torah that "an eye for an eye" should be understood figuratively, as some sort of compensation.

The difficulty evaporates when we realize that "an eye for an eye" principle only applies to exemplary punishment in the very specific situation. In such rare cases, reciprocal corporal punishment could be feasibly carried out.

The lawgiver makes his intention known by starting the Laws section (Exodus 21) with rules about Hebrew slaves. Now, that's exceedingly strange. Judaism is about laws and justice, and the Laws section is a centerpiece of the Book of Exodus, literally the central (middle) chapter of the scroll. We would expect the laws to start with major themes, such as life and murder. But eleven opening verses of the Laws detail the rights of Hebrew slaves.

Those rights were exceedingly generous even by the nineteenth century C.E. norms, let alone the ancient world's habits. Slavery of Hebrews was limited to six years. Slave girls were to be treated on par with wives.

What's the point? In the opening lines, the Laws immediately shock the reader into the entirely different moral reality. The Hebrews must isolate themselves from the old habits: from barbarity of neighboring tribes, brutality of Egypt, even from the inbuilt human egoism. At this point, Hebrews are commanded to abandon the natural human behavior of exploiting their compatriots to the utmost extent feasible. They are told to care about the most vulnerable members of their society, Hebrew slaves.

It is not that caring of Hebrew slaves is the major civil law, but it relates the major legal principle, "Love your [Hebrew] neighbor as thyself." That principle is not merely a moral piece, but a fully actionable law.

The Laws section then proceeds with common legal issues.

Murder of a man is generally punishable with execution (Exodus 21:12). In case of premeditated murder, there can be no excuses whatsoever (21:14); the intent to murder a fellow Jew undermines the society's very basis.

There is a legal innovation: manslaughter, voluntary or otherwise, is not punishable; the offender can find refuge among Levites and later in specially designated towns. The only criterion is whether the offender waited for his victim to kill. In Jewish law, generally only actions matter rather than intentions. Why this case is different, why one murder is different from another? Even the nicer modern legal system punishes for manslaughter. The reason is to be seen in the opening verses on the treatment of Hebrew slaves. In such a compassionate society, unpremeditated murder must be presumed unintentional, purely an accident which does not call for punishment.

The murderer fled to a place of refuge, but what about his clan or immediate family? In barbarian societies, they would be targeted for vendetta. Jewish law, however, contains no hint of preventing vendetta, suggesting that it was non-existent in the society. Absence of collective (clan-level) or extrajudicial retribution testifies to the Hebrews' high morality and law obedience. The law was not idealistic, but successfully converted the throng into the perfect society.

Contrary to the common misunderstanding of "an eye for an eye," bruises incurred in fights among men are not subject to retribution, but merely compensated. Exodus 21:18-19, "And when [the] men would squabble, and the man will hit his neighbor with stone or fist, and he will not die but lie in bed: If he rise up and walk outside [his house] on a support, then cleansed [from the guilt of murder] will be the one who hit, only gives [for] his idleness and shall treat, treat."

The period of acceptable illness is any. The lawgiver didn't forget specifying the period, as it is explicitly mentioned in the following verse on beating slaves.

A good reason for not treating a fighting injury as a criminal offense is that both sides are guilty: they equally participated in fight. So there is no punishment per se, but merely compensation of lost earnings and medical expenses.

The law is careful to clarify that any squabble suffices to exonerate the offender. There need not be a fight, but merely a squabble.

Now we know the punishment for murder (execution) and any injuries incurred in a squabble (compensation). What about the injuries inflicted without a fight: by surprising one's opponent or where one man is clearly stronger than another? In such situations, murder is a more likely outcome. Or, we may apply a fortiori argument: if the injuries incurred in a squabble (where both men are equally involved) are compensated, then all the more the injuries incurred in a surprise attack should be compensated. Fully conforming to the liberal ideal, Hebrew law discusses only generic situations; in contrast, modern law is concerned with specifics, thus creates a heap of highly specific legislation and, consequently, loopholes.

Next, the law deals with the most tender and valuable members of Hebrew society: pregnant Jewish women. Exodus 21:22, "If [the] men would fight, and hit a pregnant woman, and the fetuses come out, and there will be no harm [to the woman], then he will be fined, fined as the woman's husband imposes on him, and gives as they lay [on him]." Contrary to anti-abortionists' views Hebrew law does not treat fetus as a human being: killing a fetus is punishable with fine only, it is not a criminal offense such as killing a human being.

The fine is not specified here, and whether it is large or small, is a matter of conjecture. On one hand, the law carefully specifies the double and quadruple fines, and therefore leaving this fine unspecified hints at it being insubstantial. On other hand, the law uses strong language: "fined, fined" and "lay on him." My feeling is that the first option is true, and the fine is small, thus not subject to specification; strong language refers to sureness of the fine rather than its amount.

And here the Hebrew criminal law culminates. Exodus 21:23-25: "And if there would be harm [to the woman], then give a soul for a soul, an eye for an eye, etc." The tit-for-tat retaliation is prescribed only for harming pregnant women.

The legal status of women in Hebrew society vastly exceeded the men's. Maiming a man is subject to fine only, but similar harm to woman involves harsh retaliation. The legislator recognized that women are inherently more vulnerable than men and need stronger protection.

The law teaches us that men cannot claim weakness: it is their responsibility to be on par with any attacker, as they will not be awarded any compensation beyond the costs of treatment and idleness. Women are not expected to counter the attackers except by screaming (and surely must not serve in the army). The society, therefore, punishes even the innocent harm to women severely. The law enjoins the women from participating in men's fights: a woman who indecently touches a man involved in brawl with her husband, is punished.

What about the non-pregnant women? Young females are not expected to come close to men; only married women might defend their husbands. Old females were uncommon in antiquity. So the generic case was a pregnant woman.

The legislator makes sure that his intention of protecting the weak is clear by the following verses, "And if a man would strike his slave or concubine in an eye and destroys it, he will set him free for his eye. And if he would kick out a tooth of his slave or concubine, he will set him free for a tooth." How unusual is that, freeing a slave for merely a tooth! In that era and for three millennia afterwards, masters could kill their slaves with impunity.

This rule is a Jewish version of the affirmative action. According to the tradition, the rule does not apply to Hebrew slaves. Thus, Hebrew concubines are treated on par with wives (Exodus 21:7-11). Such a concubine should be set free even if her master/husband diminished her allowance of clothes. As she has her own clothes, she is a subject of property rights, and not a rightless slave. Similarly, Hebrew male slave owns his wife and children (Exodus 21:3), and so is not a slave in the regular sense. Hebrew slaves are set free at the end of six-year periods, so in effect they are temporary laborers rather than slaves.

In the case of foreign slaves, their masters own their bodies, but Hebrew slaves possess property rights: if they own their wives, then all the more they own their own bodies. Any injury done to a Hebrew slave's body should be compensated like to free men.
The legislator here solved a curious puzzle: since foreign slaves are their masters' property, a master cannot compensate his slave for injury like he would compensate a free person. Sort of fining oneself for breaking one's own instrument. That paradox surfaced in Exodus 21:20-21: murder of a slave is a punishable offense, but any other harm is not punishable as slave's body is "his master's silver." Freeing injured slaves is both ethical, instructive (to slave-owners), and the only logical way to enforce justice while respecting the property rights.

Here is the affirmative action: a Hebrew slave is only compensated for his eye or tooth, but foreign slave is released for the similar injury. The master is, in effect, fined by the tooth' cost and the entire slave' cost, respectively. Therefore the fine for harming the rightless, defenseless foreign slave is much larger than for similarly injuring a Hebrew slave.

No system of justice accounts for all the possible circumstances. Murdering a slave is a criminal offense (Exodus 21:20), injuring him permanently is a civil offense (21:26-27), but what about the situation when the slave died a considerable time after the beatings? Being dead, he cannot be released on the account of injuries, as Exodus 21:26-27 prescribes. At the same time, he was not exactly murdered, as he did live for considerable time afterwards; perhaps the blows were not lethal but his treatment was wrong? Even in the modern courts, which have the benefit of autopsy and other types of expert analysis, there is often no clear-cut answer. And so the legislator sighs, "And if he lives for a day or two, he should not be avenged, as he is [his master's] silver."

Note that the great kindness was prescribed not to the weak in general, but only to loyal (wives) or submissive (slaves). Nothing in the Hebrew law implies kindness or even restraint to enemies, but only to subjugated enemies.

The law equates hitting (21:15) and abasing (17) one's parents; both actions are punishable with death. There is no issue about murdering them: such crime is covered by generic rule of executing murderers. The law is a direct consequence of, "You shall respect your father and your mother" in the Ten Commandments. Rabbis effectively abrogated a similar law about unruly child by demanding unrealistically that both father and mother accuse him in the same voice tone. In the law, however, abasing any parent is a capital offense, no other evidence is required. The law does not sentence merely for a heated argument: only the one [continuously] abasing his parents is liable to death. How do we know it is a crime to abase any parent rather than both of them, for it is said, "his father and his mother"? By comparing this law with, "And he who is hitting his father and his mother, shall die by execution" (21:15): obviously, it is a crime to hit any parent rather than both of them.

Why so harsh a punishment? It's not because of primitive paternalistic concerns; such concerns would justify execution for insulting one's father (head of the clan) but not mother. The law is meant to strengthen the society by strengthening family. The law emphasizes family in the modern sense rather than clan. By making it unthinkable to abase mothers, the law forced Hebrews to leap into the mutually respectful society.

Now we see that Jewish law prescribes different levels of retaliation: mild for the offenses between men, harsh tit-for-tat for attacks on women, hyper-compassionate for wounding slaves, and exceedingly cruel for offending parents. What about the other nations? The Torah deals with two classes of the offending nations. One is Amalek: those who harassed the Jews; such nations must be exterminated even in the remotest generations for their past crimes, probably on the presumption that national character doesn't change and children would readily repeat their parents' sins if given an occasion.

The second class is the nations which settled the Promised Land before Jews; such nations would always remember that the land was theirs, will consider the Jews occupiers, and hate us. Unlike Amalek, they should not be wiped out as they committed no crime against Jews, but rightfully defended themselves against aggression. Jews must evict the core inhabitants (Exodus 23:31), destroy their places of worship (23:24), and God will efface them (23:23).

The raw justice mercilessly extirpates the offenders so that law-abiding Jews can live comfortable lives. Jewish criminal law is unforgiving: neither a victim, nor the society can forgive, but the offender must be punished severely. Forgiveness paves the way to repeated crimes.

Leviticus 24:19-20 suggests that Jews originally adhered to across-the-border "an eye for an eye" and that rule was later softened to apply to pregnant women only. Jews, themselves recently slaves in Egypt, hardly acquired Jewish slaves already in the Sinai. The subsequent verses deal with a settled society with houses, pastures, holes on the roads, and so on. Whatever the legislative sequence, at some point Jews were given a law that presumed goodwill among neighbors, protected the weak, and severely punished the wicked.