Q&A: What is the logic behind the prohibition of wasting seed?
What is the logic behind the prohibition of wasting seed?
Question
Hi, Rabbi.
Recently I started looking into the issue of the prohibition of wasting seed, and I got to the source in the Talmud where the Talmud derives from Er and Onan that it is forbidden to waste seed.
My question is: anyone who looks at the verses without the interpretation of the Sages will conclude that God was angry with Onan solely because he did not raise up offspring for his brother, and there is no real connection to the fact that he spilled the semen. The Sages learned from this that in general it is forbidden to waste seed, but it is very hard to think that this was the Torah’s intent. It occurred to me that perhaps the Sages forbade this because in their time scientific knowledge held that it was harmful, and therefore today the prohibition is no longer relevant. And if so, when a Sanhedrin is established, could we change this prohibition and permit it?
(And even if we assume that the Sages were right, how was Onan supposed to know that it is forbidden to waste seed? At that time there was no Torah in the world to prohibit it.)
Answer
It is very likely that the Sages understood this on the basis of reasoning, and assumed that Onan too should have understood it. It is unlikely that this was because of the harm the act causes, since the commentators connect it either to manual adultery or to something akin to murder. No one explains it as deriving from the rule of “guard yourselves very carefully” or from preserving one’s health.
Cain too was supposed to understand that murder is forbidden even before there was a command. The assumption is that prohibitions on certain acts are self-evident. The source cited for this is not always the real source. Sometimes it is merely a scriptural support. None of the enumerators of the commandments counts this as a prohibition, so it is likely they did not see it as a prohibition with a clear source.
Beyond that, even if Onan was not supposed to know this, the Torah’s description of the matter is the source, even if not for Onan himself. Just as some derive that one should not marry off the younger sister before the elder, because they did not do so in Laban’s place. Is Laban a halakhic source? The Torah’s description led them to understand that the Torah itself sees this as a proper principle.
Discussion on Answer
Fine, I explained what I had to say. As for whether a Sanhedrin today could change this—certainly. It can change everything. It could decide that there are ten primary categories of labor, or 108. Whatever seems right to them. Whether in practice they would do so is a different question.
But today it’s clear to us that a baby is not contained inside the semen, and only a very, very tiny fraction out of the thousands of sperm that come out is actually useful for having children. So does a person who has relations with his wife violate the prohibition of wasting seed? Obviously not.
I’m not saying they necessarily forbade it for medical reasons, but it could be that they had their own agenda. And on rereading the verses, I still come to the conclusion that God is angry with Onan purely because he did not raise up offspring for his brother, and that it has nothing to do with the emission itself.
But I’m still asking: if somehow a Sanhedrin were established right now, could we permit this prohibition? After all, if the Sages arrived at it through a certain line of reasoning, we can arrive at the opposite reasoning from the Sages.