Possessing Hazardous Items
In Parashat Ki Teitze, the Torah warns against possessing hazardous items: ("lo tasim damim be-veitekha") when you construct a new house, erect a fence (ma'akeh) upon your roof, and do not place blood in your house when people fall from it." (Devarim 22:8). In cautioning against possessing hazardous items, the Torah issues both positive (asei) and negative (lo ta'aseh) commandments - build a fence around your roof and do not "place blood in you house" – i.e. own dangerous objects. Are we to assume that the scope of both the positive and negative commandments are identical? Does the Torah intend to legislate against specific hazards and reiterates simply to emphasize and reinforce? Or do the positive and negative commandments refer to different situations (although possibly allowing for some degree of overlap)?
The most apparent distinction between these two possibilities concerns the relevance of the mitzvat asei to hazardous objects. The literal reading of the verse suggests that the asei only mandates building a wall around a roof. The Sifrei extends this commandment to other structural hazards- pits, alcoves and other dangers must be fenced in or covered as well. However, would the asei also demand elimination of a hazardous animal? Or would such an action be required solely by the lo ta'aseh which, formulated in general terms, clearly applies to all dangers? An interesting gemara in Bava Kama seems to adopt the latter approach. Typically if one person preempts another in the performance of a mitzva, he must pay ten gold coins to the victim. For example, the gemara in Chullin (87a) states that if Shimon preempted Reuven and covered the blood of the latter's shechita, he must pay this fine. Similarly, the gemara in Bava Kama (91b) requires payment from someone who eliminated another person's animal which was 'slated for death.' The gemara is unclear, however, as to the conditions of an animal 'slated for death.' The Ra'avad asserts that the gemara is referring to a 'shor ha-niskal' – an animal that killed a human which must be executed by Beit Din. Rashi, however, claims that the gemara refers to any dangerous animal- even if it has not yet murdered, and has not been legally condemned. Evidently, according to Rashi, the mitzva being preempted is the asei of ma'akeh. This suggests that, in Rashi's opinion, the mitzva of ma'akeh does apply universally to any hazard, and not just to structural objects. In contrast, the Yam shel Shlomo disagrees, and claims that merely preempting the avoidance of a lo ta'aseh would obligate payment – implying that the positive commandment of ma'akeh does not apply to general objects, but the negative commandment of not placing blood upon your house does. Removing a dangerous animal fulfils the negative commandment, and preempting that fulfillment obligates payment. According to the Yam shel Shlomo, we could therefore differentiate between the asei which only governs structures, and the lo ta'aseh which applies more broadly.
Like the Yam shel Shlomo, the Rambam's classification of these halakhot does imply a difference between the asei and the lo ta'aseh. In Hilkhot Nizkei Mammon, chap. 11, he first cites the asei of ma'akeh, and defines the mitzva as a requirement to fence in a roof. In halakha 4 he extends the scope of the asei to all hazardous items – specifically, PITS and WALLS. Toward the end of halakha 4, he concludes: "and likewise any hazard which imperils life must be removed… because of lo tasim." Seemingly, Rambam expands ma'akeh to include pits and walls, but not portable items. The portable items are only encompassed by the lo ta'aseh of lo tasim. (It should be noted that regarding dangerous objects Rambam DOES acknowledge an asei which accompanies the lo ta'aseh- but not the asei of ma'akeh. He develops a novel position that the Torah instructs us to eliminate any form of life-threatening danger based on the verse of "Guard yourself, and watch yourself very carefully…" (Devarim 10:4). Though in context the verse instructs us not to forget the epic events at Sinai, the Rambam reads the verse as demanding safe and prudent behavior. Possessing dangerous items would constitute a violation of this asei. However, the Rambam does not apply the asei of ma'akeh to non-structural objects.)
An additional distinction between the lo ta'aseh and the asei emerges from a statement of the Sefer Ha-Chinukh. The verse refers to "damim," and as a result, most Rishonim claim that both the asei and the lo ta'aseh only apply to items which are life-threatening. This position may contradict the gemara in Bava Kama (15b), which applies lo tasim to fierce dogs and faulty ladders- which would not seem to be life-threatening. One way to reconcile these Rishonim with this gemara would simply be to explain that these items can theoretically jeopardize life. Alternatively, the Rav zt"l claimed that even though the Biblical prohibition applies only to life-threatening items, the Rabanan decreed against all hazards. The gemara in Bava Kama never claimed that possession of a vicious dog violates the Torah's prohibition, but rather claimed that it violates the Rabbinic which expands the Biblical prohibition.
The Chinukh (546) explicitly claims that items which may cause physical harm, but which are not life-threatening, are included within the Biblical prohibition of lo tasim. This position may be challenged based on a gemara in Bava Kama, which determines that only a pit that is ten tefachim deep makes its owner liable for any deaths that it causes. This conclusion is based on the halakha that a ma'akeh must only be built for heights of ten tefachim and higher. This gemara implies that a ma'akeh is only necessary to prevent death – and thus only a height of ten tefachim, which can cause death, must be fenced in. How would the Chinukh – who extended the lo ta'aseh of lo tasim to all types of hazards- understand this gemara?
The Devar Avraham (1;37;25) answers that the Chinukh would distinguish between the asei and the lo ta'aseh. The positive commandment of ma'akeh would only obtain to life threatening situations- for example a height of ten tefachim or more. The lo ta'aseh, though, applies more universally to all sorts of perils. This understanding of the Chinukh's position provides yet another example of a difference in scope between the asei and the lo ta'aseh.