Eruvin 11

Today’s daf (Eruvin 11a-b) discusses the צורת הפתח (‘a form of a doorway’ – consisting of two vertical sideposts [לחי], on which sits a horizontal beam, pole or twine [קורה], to create ‘a form of a doorway’) which operates as a substantive halachic boundary such that an opening with a צורת הפתח is considered to be halachically ‘closed off’.
However, for a צורת הפתח to be effective it needs to meet certain criteria, and this leads the Gemara to consider the essential properties of an effective צורת הפתח – while drawing a comparison between the laws of שבת (where a boundary is required to carry), and the כלאים prohibition forbidding the sowing together of different seeds (or in this case, the growing of vines alongside other produce where a boundary is needed to separate between them).
We are told in Eruvin 11a that a certain man from the valley of Beit Hortan created a צורת הפתח in his field by placing poles in the ground and by stretching a vine on top of them, in order to create a boundary between his vines and the other produce that he was growing. Having heard of this incident, Rav Yochanan remarked that while this type of צורת הפתח is an effective boundary for the כלאים prohibition, it is an insufficient boundary for the laws of שבת. Constrasting this, Reish Lakish remarked that this boundary is effective both in the case of כלאים, and in the case of שבת.
But then, in Eruvin 11b, we are told of an incident that occurred over a century beforehand when Rabbi Yehoshua – who was already considered to be an expert in the laws of כלאים – went to study Torah with his teacher Rabbi Yochanan ben Nuri who was sitting between some trees. Upon arriving, Rabbi Yehoshua stretched a vine from tree to tree thereby creating a צורת הפתח, and he then asked his teacher a question relating to the laws of כלאים, namely: ‘if vines are here [on this side of the צורת הפתח], is it permissible to plant other crops here [on the other side of the צורת הפתח]?’
Significantly, Rabbi Yochanan ben Nuri’s response to the question presented by his student distinguishes between using a צורת הפתח for a space larger, or smaller, than ten amot (approx. 5 metres) which became an important factor in the later halachic discussions between Rav Yochanan and Reish Lakish. However, as numerous commentators point out, this story is somewhat curious since Rabbi Yehoshua is clearly identified as being an expert in the laws of כלאים, and since – by virtue of the fact that Rabbi Yehoshua first stretched the vine to construct the צורת הפתח and only afterwards asked his teacher his question – it strongly suggests that Rabbi Yehoshua already knew that a צורת הפתח of this form was an effective boundary for the כלאים prohibition. So why did Rabbi Yehoshua ask his teacher a question for which he probably already knew the answer?
Having thought about this for a while, I believe that the reason for him doing so is that, given the later discussions between Rav Yochanan and Reish Lakish (who contrast the laws of כלאים with the laws of שבת), and given the response of Rabbi Yochanan ben Nuri (who doesn’t merely answer Rabbi Yehoshua’s question of whether such a צורת הפתח is effective, but who adds an important distinction to the ongoing halachic conversation concerning the size of space where such a צורת הפתח is halachically effective), Rabbi Yehoshua was trying to ask a question that he didn’t quite know how to formulate. Meaning, while it seems clear that Rabbi Yehoshua probably knew that such a צורת הפתח could be used as a boundary for כלאים, he wasn’t absolutely sure of some other halachic details relating to the usages of a צורת הפתח – and especially the usages of a צורת הפתח constructed from vine. So he asked his teacher a question that he probably knew the answer to, which then evoked an answer to a question which he hadn’t specifically asked which was, in later generations, then applied to spheres of Jewish practice far broader than his particular area of expertise.
An oft-used phrase relating to those with an expertise in one particular sphere is that they are – at times – unable to ‘see the forest for the trees’, and as an expert in the laws of כלאים, it should be noted that Rabbi Yehoshua was deeply immersed in the concept of drawing and fixing boundaries between different species and produce.
But unlike the laws of כלאים, there are plenty of times when one area of Jewish law does cross-fertilize another, but to see this, you need to see the forest for the trees. And this is why I think it is of significance that we are told how Rabbi Yehoshua went to study Torah with his teacher Rabbi Yochanan ben Nuri ‘who was sitting between some trees’ – because he didn’t come to his teacher to ask a specific question about כלאים for which he was likely familiar, but instead, to learn from his teacher who had a broader perspective.
Far too often we don’t ask questions to others because we think we know the answer to that particular question. But what we often forget is that – like a vine – a single question can grow in many different directions – and like Rabbi Yehoshua – the person we have turned to may be able to hear questions we haven’t clearly asked, and see things that we cannot clearly see.