leniency depending on the circumstances. One series of questions concern the way in which these presumptions interact. Another is the more fundamental question of how presumptions work. That is, does a presumption have the effect of assimilating the doubtful cases to the certain cases in all respects, or are doubtful cases a third category with its own special laws, alongside the certainly included and the certainly excluded? Although each section focuses on a specific Halachic principle, invariably other principles are brought up and discussed. These principles involve focal points that have applications throughout the entire Rabbinical corpus. Heller's method is to test each principle against a variety of Talmudic passages. If the concept would cause a difficulty in the passage (e.g. the concept should apply and doesn't), Heller resolves the difficult by demonstrating that for whatever reason this passage doesn't fit underneath the rubric of that particular concept (see Casuistry). In this way the exact boundaries of each principle are clearly defined, thus clarifying the exact applications of each principle. Section One The first section analyses whether the concept of "A doubt in a biblical issue is dealt with stringently" is actually a biblical concept itself or whether it is entirely of Rabbinic origin. This section continues into a discussion of the principles that, if there is a doubt concerning a case of spiritual impurity, if this occurred in the public domain we rule leniently and in the private domain stringently (Sotah 28b). Finally, the ruling that in a case of Sefek Sefeika - a case of doubt in which one side of the question is itself subject to doubt - we rule leniently is explained. The reason is that since most sides of this question lean to the lenient side, the principle of Rov - that we follow the majority - is called in and we rule leniently. Section Two The second section analyses the presumption of chazakah. Chazakah is the presumption that in case of doubt one may assume that the physical or legal status of the object (or person) in question remains constant. At this point the focus is on Chezkat Ha'Guf - that the physical status of the object remains unchanged - and Chezkat Mammon - that we assume that an object belongs to its current possessor unless otherwise proven. The relative strengths of these two Chazakot are compared and contrasted. Also the importance of the