Even though halakha eschews distinguishing between serious prohibitions and less severe ones, one particular aveira is selected for special mention. Among the first five [of the ten] commandments (generally regarded as bein adam la-makom) appears the prohibition of 'shevuat shav' - literally an oath taken in vain. The pasuk describes that God will not 'cleanse' a person who violates this crime (Shemot 20:6; Devarim 5:10). Based on this warning, the Rambam recognizes that the teshuva process for this sin (as well as classic shevuat sheker) is significantly more complicated than for other violations. This shiur will explore the nature of the prohibition against shevuat shav.
The Torah contains four sections describing the various prohibitions surrounding improper oaths. The above section dealing with shav is actually repeated twice (in each listing of the ten commandments). The Torah twice describes the various laws regarding shevuat sheker (false oath). Parashat Vayikra (perek 5) addresses the unique korban offered by someone who inadvertently issues a false oath, while parashat Kedoshim contains the basic warning against these types of oaths - "lo tishavu vishmi la-shaker" (Vayikra 19:12).
The first mishna in the third perek of Shavuot describes four different forms of false oaths: someone who swears that he did something which he didn't; someone who swears that he did not do something which he in fact did; one who swears to perform something and he doesn't; one who swears not to do something and ultimately does.
Returning to the concept of shevuat shav, one question immediately presents itself: what is the relationship between a false oath (shevuat sheker) and a shevuat shav? By separating these two forms of shavuot into different sections, does the Torah intend to accentuate their conceptual disparity? Or do they share certain basic patterns allowing for minimal differences that are reinforced by the distinct parshiyot. Said otherwise, would we describe a shevuat shav as literally an oath taken in vain without any utility or purpose - a description that is fundamentally different from a shevuat sheker? Or would we view a shevuat shav as a more intense form of sheker with slightly separate halakhot but essentially the same character? Indeed, the mishna in Shavuot (29a) affirms that while a korban is offered for negligent shavuot sheker, no such korban is offered for shavuot shav. Is this discrepancy reflective of a broader thematic gap between the two, or merely a slightly nuanced difference?
While the conceptual issue can be traced to the sequencing of the various parshiyot, it can also stem from a linguistic question. The term 'shav' can possess two different meanings in Tanakh. More often, it refers to something without value or utility. Sometimes though, it refers to something which is false - see for example the pasuk in Va'etchanan that prohibits false testimony: "lo ta'aneh ve-rei'akha eid SHAV" (Devarim 5:16). By stipulating the prohibition of a shevuat shav, did the Torah create a new independent category or did it merely establish a more severe form of sheker?
The most compelling difference in this regard can be sensed in an interesting discrepancy between the list of shavuot shav in the Bavli and the list provided in the Yerushalmi (a list that the Rambam adopts). The Bavli (Shavuot 29a) cites three examples of shavuot shav:
1) denying something plain and obvious (swearing that a stone is water)
2) swearing about the impossible (swearing that you saw flying animals)
3) swearing to suspend a mitzva (swearing against eating in the Sukka)
In each of these cases, one might claim that the prohibition stems from the severe and preposterous sheker latent in the oath. Arguable or evolving sheker (I will eat, I won't eat, etc.) are included in the prohibition of shevuat sheker while undeniable and ridiculous sheker is subsumed by the prohibition of shav. The Yerushalmi, however, adds a fourth example of shevuat shav: affirming the obvious (swearing about a rock that it is indeed a rock). If we include this case as shav, we cannot associate shav and sheker; this oath contains no element of sheker. Instead we must define shav as pointless and useless oaths; clearly affirming the obvious is the truest form of an oath that lacks any utility.
A second issue pertaining to the scope of shevuat shav is addressed by the Amoraim. The gemara in Shavuot (20b) cites a peculiar position of Rav Dimi. He agrees that oaths about the future (I will or will not act) are clearly in violation of shevuat sheker (if not implemented). Oaths about the past however (I did or did not act) are a violation of shevuat shav. Rav Dimi effectively adds a fourth shevua to the list of shav quoted by the mishna. It might be difficult to define this oath (concerning a past act) as pointless since the topic of his oath is not common knowledge. By issuing the oath he is trying to convince his audience about the event in question. We do, however, recognize false oaths about past events as a more severe form of sheker. The sheker factor in future oaths is uncertain. Based upon his future behavior, his current oath will either be proven accurate or false. Oaths about the past, however, are immediately true or false. We might not be immediately aware of their identity as we are in the case of denying or affirming the obvious, but objectively the possible sheker is automatic. One can easily cast this type of shevua as an intense sheker and describe it as shevuat shav. Evidently, Rav Dimi viewed shav as a variety of sheker and was willing to extend its scope to false oaths about the past. The gemara subsequently cites Rav Avhu's position which is the more conventional and ultimately more accepted one: ANY shevua about non-obvious issues (future OR PAST) are categorized as shavuot sheker, while obvious oaths (or oaths about the impossible or canceling mitzvot) are catalogued as shav.
This question might have propelled an interesting machloket between Rashi and the Rambam. The gemara in Shavuot (25a) concedes that an oath about someone else's future conduct is not a viable oath. Since I cannot control its outcome I cannot formulate such an oath. Rashi (s.v. lesei) claims that this oath (which does not impact upon someone else's behavior) is also considered a shav. The Rambam (Shavuot 5:1) argues as the Kesef Mishna explains: since the oath might be proven true (i.e. the other person might indeed eat the bread you swore he would eat), it cannot be defined as shav. Rashi might have defined shav as pointless or vain. A shevua about someone else's behavior can clearly be described as pointless since the person issuing the oath cannot determine its fulfillment. The Rambam could conceivably have defined shav as extreme sheker. Since this sheker is still in process and might never materialize we cannot consider it extreme sheker and a violation of shav.
Note: This explanation of the Rambam would seem to contradict the aforementioned comments about the Rambam's position vis-a-vis the discrepant listings of the Bavli and Yerushalmi. By embracing the Yerushalmi's example of a shevua that affirms the obvious truth, the Rambam would seem to avoid defining shav as extreme sheker. We might have to adjust our overall perspective of the Rambam's position.
Another interesting ramification of this question pertains the overall scope of the prohibition "lo tisa shem Hashem Elokekha..." mentioned in parashat Yitro (Shemot 20:6). The gemara in Berakhot (33a) comments that one who recites an incorrect beracha has violated the prohibition of "lo tisa shem..." Many Rishonim declare this prohibition to be miderabanan in nature. By contrast, the Rambam (Berakhot 1:16) claims that these types of berakhot entail a mideoraita prohibition. By extending the issur of "lo tisa shem" to inappropriate berakhot, the Rambam might again be defining shav as pointless mention of God's name and not some form of intense sheker. One cannot locate sheker in unnecessary berakhot. This position would closely parallel the Rambam's accepting the Yerushalmi's case of affirming obvious truth as a case of shav.