There is an old problem, which deals with one of the most fundamental aspects of דיני ממונות, monetary laws, within the broader framework of Jewish law. There is the well known principle that המוציא מחבירו עליו הראיה; if one wishes to extract money from his fellow, the burden of proof is upon him. This is applicable to the extent that the courts will not extract payment even if the defendant himself is unsure whether he is in the right. For example, if Berel claims that Shmerel borrowed $100 from him, and Shmerel says he cannot recall what occurred on that day, the Halakha says that he is not obligated to pay until Berel provides sufficient evidence that the loan did actually occur. This is certainly within reason, for if Berel were to be able to force Shmerel to pay him simply by virtue of Shmerel’s lack of knowledge, then this would provide a sure means for any disreputable individual to steal money with the law on his side. For anyone can claim, for example, ‘You dented my car without realizing it’, and generally in this situation the honest defendant will have to concede that he does not know. It is thus reasonable to say that the one who wishes to extract money from his fellow must first sufficiently back up his claim.
The problem with this principle is not a logical problem, but rather that it would seem to contradict another basic Halakhic rule. The Halakha says that ספק דאורייתא לחומרא, when in doubt about a Biblical obligation one may not be lenient. For example, if one is unsure whether or not he said Grace after Meals, he is required to recite it. If one is unsure whether or not something is kosher, he may not eat it. One may rely on a probability in these cases, but when the only factor of consideration is the doubt of the person, he is required to be stringent upon himself. Moreover, in such a case the courts treat him as one with a standard obligation, for he has no right to be lenient. Ergo, the question is as follows: Why is it that this most basic rule seems not to apply to דיני ממונות? There is definitely a Biblical injunction; indeed, it is the seventh of the Ten Commandments which states לא תגנב, do not steal; yet we have noted that when one is in doubt, the courts do not compel him to pay. Why does the Halakha of ספק דאורייתא לחומרא not get activated here; why is one not obligated to be stringent about monetary matters just as every other Biblical command which one is doubtful about?
There have been many attempts to solve this age old problem, but to me none stand out as does the answer presented by Rabbi Shimon Shkop. He provides a fascinating insight which not only solves the problem at hand, but completely revolutionizes the concept of דיני ממונות as they pertain to Halakha in general. Although he published the idea in his two volume magnum opus שערי יושר, I have heard it explained (or not explained) in several different ways, but the following is what I took from it, with some of my own flavoring added (whether it is נותן טעם לפגם or לשבח has yet to be determined):
In the Torah we find laws about trees. We also find laws about animals. How is one to know what a tree is or an animal is? Such knowledge obviously must be arrived at before one can attempt to observe any of the laws. Many laws of Kashrut require a more-than-basic knowledge and understanding of biology and anatomy. The Torah does not generally define for us what a tree or an animal is, but rather guides us with laws about those things which are supposed to be axiomatic. It is clear that the Torah was not written in a vacuum, but that it was intended for a world of experience, where we can see a certain thing, know what it is, and then look to the Torah for direction. So it is, explains R. Shimon, with the prohibition against theft. There cannot be a prohibition of לא תגנב without a prior understanding of the laws of ownership. Which leads us to a fascinating conclusion: There must be an accepted system that defines ownership before the Torah; there must be an accepted concept of ownership before there can be a prohibition against theft. I don’t own it because you aren’t allowed to take it; I own it and therefore you aren’t allowed to take it. However, this immediately begs the question: What defines my exclusive ownership of an object if there is nothing telling you not to take it? The answer, says R. Shimon, is that the Torah recognizes the social contract of a community. It is perfectly within reason for a society to establish laws of ownership, in order to ensure the possibility of a stable community. Therefore, the object is mine because the laws of the social contract say that I have exclusive rights to it and not because the Torah says so; the Torah only added by redefining your act of theft as something wrong.
This being the case, there is an easy solution to our problem. The prohibition of לא תגנב does not get off the ground until the social contract says that the object in question is exclusively owned by someone other than the current possessor. Therefore, if the courts rule that המוציא מחבירו עליו הראיה, even if I am uncertain as to the truth of the matter, there is no room for the prohibition of לא תגנב. The dictum ספק דאורייתא לחומרא has no place here, for one is only required to be stringent when there is a possibility that his actions may violate a Biblical law, but here the law does not begin if the courts cannot obligate me to pay.
This solution also provides insight into the law of הפקר בית דין הפקר, that the courts can render an object ownerless. The sages determined through reason that it is necessary in a stable community for the enforcers of the law to have some power over the people. Therefore, they instituted a clause in the social contract, that of הפקר בית דין הפקר. This did not in any way constitute a departure from the established precedent, let alone a departure from the Biblical injunction of לא תגנב, since it was always in the hands of scholars and sages, or more fundamentally – the courts, to determine what falls into the category of לא תגנב.