The Talmud discussed the issue of carrying a chair or a bench across the ground, considering that it is likely to cause a furrow in the ground. Ula is quoted as saying that there is a dispute if this is permitted when the chairs involved are small; when they are big, all agree it is permitted. Tosafot comment that this text, counterintuitive as it sounds, is accurate, and should not be replaced with “all agree it is forbidden”. The question of which text is correct is taken up by other commentaries as well (see Ritva; Ramban; Kessef Misheh 1:5, citing Ramach; Yereim, 274).

As noted, the first version does appear counterintuitive; if an action is prohibited because it will definitely bring about a melakhah (psik reisha), larger chairs are even more likely to cause furrows than smaller ones. Rabbeinu Dovid (Pesachim 25b) explains that in the case of the larger chairs, it is impossible to transport them without dragging them; thus, a furrow caused by that dragging can be attributed to a completely unintentional action (davar sh’eino mitkavein). However, smaller chairs can be transported without dragging them; thus, dragging them, and consequentially creating a furrow, has the stain of negligence.

As noted by the Pri Moshe (Shabbat, 4:4), at issue here may be the question of why it is that “psik reisha” creates responsibility even when the result is unintended. There appear to exist at least two possibilities: a) as the result will definitely occur, it cannot legitimately be considered unintended; b) the result becomes an extension of the original action. If the first explanation is dominant, it seems logical that larger chairs, that will even more definitely create furrows, are without question prohibited. If, however, one uses the second interpretation, it might be argued that the secondary result only becomes a part of the initial action when the actor had the possibility of doing that action without it; thus, the consequence is considered deliberate. If, however, there was no way of performing the action without the consequence, that consequence remains unintended.