Jewish law is generally divided into three distinct areas: issur v’heter, ritual law; dinei mammonot, monetary law; and tumah v’tahara, laws of purity and impurity. Just as the laws regarding criminal and civil law differ—the former requiring evidence beyond a reasonable doubt and the latter a balance of probabilities—each area of Jewish law has its own rules and procedures. Hence, our sages note, “One cannot derive principles regarding ritual laws from [those of] monetary law”. Whereas, for example, regarding areas of issur v’heter the testimony of one witness is determinative, when it comes to monetary law, two witnesses are required before one could extract payment.
Yet the third area of Jewish law, that of tumah v'tahara— virtually irrelevant today—is the largest, and the one that, during Temple times, was perhaps the most relevant. It impacted on almost every aspect of life: what one could eat, with whom one could eat it, where one could sit, how one would celebrate the holidays, where one might live, with whom one could sleep and for some, even with whom they would interact.
Of the six orders of the Mishna, seder Taharot, dealing with the laws of purity, is by far the largest with some 1,003 mishnayot. The next largest seder, that of Nezikin, has a mere 685 mishnayot. And many mishnayot in the other sedarim deal with the issues of tumah v'tahara and could easily have been included in seder Taharot.
People, vessels, food and drink are all susceptible to the laws of tumah. Even the corpse of an animal can transmit tumah. To many, this all sounds a bit strange, and I don’t think I am going out on a limb by suggesting that few lament the inapplicability of these laws today. Yet these laws were much beloved and happily embraced by many. Those who found little meaning in these laws could, for the most part, ignore them. That is because it was only regarding entering the Temple grounds and eating sanctified food that, technically speaking, one had to be careful regarding the laws of tumah and tahara. As long as one had no intention to enter the Temple or eat of its sacrifices (or terumah), there was little need to worry about these laws. There really is nothing wrong in being tameh. Even a kohen, who is prohibited from contacting tumah, was required to do so in order to attend the funeral of a relative.
Nonetheless, maintaining the ability to enter the Temple at will resonated with many. Moreover, as terumah had to be eaten in a state of purity—both the food and the person—and as all farmers had to separate terumah from their produce, sharing of food between a chaver, one who was careful about the laws of tumah and of tithing, and an am haaretz, one who was not, was potentially problematic.
Beit Shammai went so far as to rule that one should “sell his olives only to a chaver” (Demai 6:6), lest an am haaretz squeeze the olives while in a state of impurity, causing them to become tameh—and it is not proper to cause tumah in the land of Israel). Beit Hillel allows one to sell to anyone as long as the buyer is careful about the laws of tithing. Since food cannot become tameh unless it comes in contact with one of seven liquids—wine, blood, olive oil, milk, dew, date honey and water (known by the acronym yad shachat dam)—one can sell dry olives to all. While it is very likely that the buyer will squeeze the olives, leading to tumah, Beit Hillel relies on the farfetched possibility that he won’t. They preferred to break down potential barriers between people. It was and is not easy to balance one’s desire for religious growth with the need to interact with those who have no such desire. And yet, the Mishna concludes that the “tzenuei Beit Hillel, the modest ones of Beit Hillel, would act in accordance with [the view of] Beit Shammai”.
Why this is so is perhaps related to the nature of tumah. Death is metameh, defiling, and Judaism celebrates life. The closer one’s encounter with death, the greater the level of tumah. Thus, a dead body is considered avi avot hatumah, the grandfather of impurity, with tumah decreasing as we get further and further away from this prime cause.
The balancing act between avoiding tumah without distancing those who are not careful regarding tumah and tahara is evident during the lead-up to and during the shalosh regalim. The Mishna (Chagigah 26a) teaches that during the shalosh regalim, all—including amei haaretz—are assumed to be tahor and hence, anything they handle retains its status of purity. Yet once the holidays are over, that assumption is no longer considered valid. Thus, when Yom Tov is over, all the vessels of the Mikdash must be brought to the mikvah—because we fear that they did indeed become tameh.
On a practical level, a merchant may sell wine handled by an am haaretz during the pressing season; but once the season ends, we must assume that that same wine is now tameh. More startling, that same wine regains its presumption of tahara when the next pressing season approaches.
This is just one example of how no legal system can reflect absolute truth. Legal and halachic truth is, at times, most contextual, with a range of factors beyond the theoretical law impacting on the decision. Thus, the same piece of meat might be declared fit for consumption for one person, but not for another. Such a scenario may play out in a case when the meat in question belongs to a poor person and it is Friday afternoon, as opposed to a person of greater means on a Wednesday. A bifurcated ruling reflects the basic uncertainty a human being must have in making complex decisions. Absolute truth can be found only in the Divine.
 A single witness confirming the claim of the plaintiff would compel the defendant to take an oath that they do not owe the money—and if they refuse, they would then be compelled to pay the monies in dispute.
 A korban shelamim, the only korban from which a non-kohen could partake, could be eaten anywhere in Jerusalem.
 While the term “am haaretz” has various meanings in the Talmud depending on the context, the simple and overarching meaning seems to be one who was not careful to avoid impurity such that there was doubt as to whether he had properly tithed his food.
 An example today might be the propriety of someone who eats only glatt kosher meat accepting an invitation from a friend who likely is not strict in this matter.
 Many non-observant (and observant?) Jews are under the mistaken notion that these laws relate to cleanliness. It is the fear of this misconception that is the basis of a minhag quoted by the RaMah (Yoreh Deah 201:75) that, after going to the mikvah, a woman should not immediately shower (i.e., at the mikvah), lest people say that “these [mikvah] waters do not purify, but rather these and those [shower] waters purify” (Shabbat 14a).