1,802. Why the Witnesses Must Sign Together

Hilchos Geirushin 9:29

The reason the Sages said that witnesses to a get should only sign in one another’s presence is out of concern that a man might tell many people to all sign a get (i.e., as witnesses). If witnesses could sign without the others being present, two might sign it and the woman might take it under the mistaken impression that it doesn’t need any more signatures. In this case, however, the get would be invalid because the husband’s condition hasn’t been met.

Hilchos Geirushin 9:30

Let’s say that a man tells three people – including a father and a son – that two of them should write, sign and deliver a get to his wife. The get is valid regardless of whether the father or the son signs with the other person. This is because one is permitted to assign a son as his agent instead of the father.