What is the best way to determine a ruling in Jewish law – to learn the rules from a teacher or to see him act on a given issue or question?
This question is a point of disagreement between amora’im in our Gemara. The Rashbam explains that each of these has its own unique advantages and disadvantages. When a student sees his teacher acting, he cannot know all of the details and facts that may be unique to this case. Furthermore, as the Ritva points out, perhaps this is a hora’at sha’ah – a one-time ruling made for a specific reason. On the other hand, actually acting on a question is a much more powerful statement about the certainty of the ruling than is a verbal statement. Such a ruling can be viewed as definitive, unless of course, there was a clear statement indicating that it was not appropriate in other cases or settings.
The Gemara quotes a baraita that rules on this issue. According to the baraita, the halakha may not be derived either from a theoretical discussion or from a practical decision unless one has been told that the halakha is to be taken as a rule for practical action (halakha le-ma’aseh). Once a person has asked and was informed that a halakha was to be taken as a guide for practical action, he may base future decisions on this precedent, provided he draws no comparisons.
The Gemara then limits this caveat “provided he draws no comparisons” only to cases like tereifot – recognizing a diseased animal that is not kosher – where damage to one organ may be fatal, while the same damage to a different organ may not be fatal. Otherwise it is commonplace that legal decisions will be based on precedent, parallels and comparisons, for, as the Gemara says kol ha-Torah kulah damuye me-daminan lah – the entire legal code of the Torah is made up of comparisons. The Ramah explains this line as meaning that it is obvious that no law book can contain all of the different possibilities that a person will face, and the only way to decide a legal question is by inferring from one case to another.