The gemara[2] tells of an Amora who chopped wood after Shabbat before reciting Havdala, but only after reciting an informal Havdala (which we call HaMavdil). We accept the opinion that this declaration that HaShem has distinguished between holy and mundane days is recited without HaShem’s Name.[3] In any case, it is agreed that before reciting some form of Havdala (over a cup, in Ma’ariv, or HaMavdil), it is forbidden to do melacha. Therefore, if you know that the taxi driver has not employed any of these options, you are arguably facilitating his transgression, which it is forbidden to do under the general category of lifnei iver – placing a spiritual “stumbling block” before the blind.”[4]
We should note that the Rama[5] cites the opinion of Rabbeinu Yerucham that some melachot (e.g., lighting a flame and carrying) are permitted before any form of Havdala, and only more “complete” melachot are forbidden (e.g., weaving and writing). While the Rama prefers the stringent opinion, it would not be forbidden to enter a taxi if the driver is acting in a manner that is permitted according to a legitimate opinion.[6] The question is thus how to categorize driving. The Tzitz Eliezer[7] assumes that driving a car is considered serious enough work for even Rabbeinu Yerucham to forbid it. This is not obvious, as the Taz[8] says that the classification depends if it is work that is usually done by a skilled worker. This would seem not to apply to driving, as most people drive. The Mishna Berura[9] says that the classification depends how much toil is involved, but this also does not seem to apply to driving. Perhaps, the Tzitz Eliezer is bothered by the taxi’s professional context or by the fact that driving is an acquired skill that requires ongoing concentration.
The major discussion is about the nature of the prohibition of melacha before Havdala. Is it that the prohibitions of Shabbat continue until one ends them (just as one can start Shabbat with a declaration on late Friday afternoon)? Or is that the work is permitted from the perspective of Shabbat, but since there is a mitzva to honor Shabbat as it leaves with Havdala, it is forbidden to commence work before fulfilling that mitzva? Rabbeinu Yerucham[10] seems to take the latter approach, which explains why some melachot are permitted before Havdala in his view. There are indications from the gemara that this is the correct outlook.[11]
If the problem with doing melacha before Havdala is indeed one of postponing the mitzva and not a matter of transgressing a more standard aveira, then there is strong room for leniency. There are many sources that indicate that lifnei iver does not apply when the problem is somewhat weak or indirect.[12] The Tzitz Eliezer[13] adds an interesting twist. If the problem is the delay of the mitzva, then it does not apply to one who has no intention of doing the mitzva at all. He reasons that if we did not make that assumption, it would be forbidden at many times of the day to feed non-daveners (even if they will make berachot) because it is forbidden to eat before tefilla. This observation could be reconciled according to the thesis that lifnei iver does not apply to indirect or weak violations.
Rav Shternbach[14] prefers the approach that there is a continued Shabbat prohibition of melacha until Havdala is recited. Nevertheless, he maintains that lifnei iver does not apply because the taxi driver is continuing to do the same melachot – those entailed in driving – that he was doing before he was hailed. (This reasoning would not apply in the case of a car service that works only when called.) Further development of the concept of lifnei iver on the Torah and Rabbinic levels is beyond our scope.
According to the approach that the Shabbat prohibition continues until Havdala, the problem may also be avoided or mitigated by the practice of some[15] to get the driver to say “Shavua tov,” which might indicate his interest that Shabbat no longer be with him and serve on some level like HaMavdil, thus suspending the continuing prohibition.
For one or more of the reasons above, it should not be surprising that several poskim[16] rule and standard practice is that one may call, hail, or get into a taxi with a driver who did not recite any form of Havdala.