By: Rabbi Avi Lebowitz
The Gemora says that if partners steal they are both liable, but if Reuven asks Shimon to steal for him, only Shimon is liable.
Rashi explains that the case of partners stealing is when one partner does the act of stealing for both of them. Since he does it on behalf of both of them, they are both liable.
Tosfos disagrees because we would only say that one cannot be an agent for a transgression on the act of shechitah to be liable four or five, but on the act of stealing, even if Reuven and Shimon are partners, we would not say that Shimon can serve as Reuven’s agent to make Reuven liable for stealing. Therefore, the only case that Reuven would be liable is when he commits the act of stealing together with Shimon.
The Maharitz Chayus points out that this is difficult even according to Tosfos. Why would we say that when Reuven and Shimon pick it up together - since he acquires it for himself, he may also acquire it for his fellow? Even when they steal it together, since we have a principle that one cannot be an agent for a transgression, Reuven is not able to serve as Shimon’s agent to steal it, and Shimon cannot serve as Reuven’s agent, so it should be considered from each one’s perspective as if the other half of the cloak is still lying on the ground and they cannot acquire it?
He explains based on the Sm”a (C.M. 182), who says that one cannot be an agent for a transgression is based upon the idea that the sender doesn’t really expect the agent to violate the prohibition, because he knows that the agent should listen to Hashem rather than him. This only makes sense in a case where the sender maintains his innocence, but in our case, where both Reuven and Shimon are doing an act of stealing, they aren’t innocent and cannot claim that they didn’t expect the other person to follow through with the agency of a transgression. Therefore, in the case where Reuven and Shimon are doing the transgression together, we say that one can be an agent for a transgression and each one serves as the agent of the other to help him acquire it.