When a beit din – a Jewish court – needs to establish facts in order to make a decision, the preferred method is to listen to the testimony of eyewitnesses and rule according to the statement that they make. The principle taught by the Torah is that testimony of two witnesses is accepted as definitive (see Devarim 19:15), and in the words of the Talmud, trei ke-me’ah – if two witnesses testify, it is as though one hundred did.
What if two pair of witnesses come into court and each tells a different, conflicting story?
In such a case the Gemara rules that we must use other methods in order to reach a conclusion on how to decide the case. The Gemara’s suggestion is to rely on hazaka – we accept the status quo ante, i.e. that the situation has not changed – until we find compelling evidence that suggests otherwise.
The case presented by the Gemara to illustrate this rule is that of a man named Bar Shatya who suffers from a psychological condition where he is sometimes healthy and lucid, but when he suffers an attack, he is considered a shoteh – mentally incompetent. With such illnesses, sometimes attacks come with great regularity; other times a particular incident may trigger an attack. Still, there may be lengths of time when no symptoms exist whatsoever, and the person is completely healthy. During those periods, the halakha respects the individual’s health, obligating him in mitzvot and accepting his actions as valid according to Jewish law. Nevertheless, it is sometimes difficult to ascertain what his mental condition is simply by looking at or speaking with him, and it is necessary for the court to establish what his state of mind was when a given event took place.
If Bar Shatya sold land, for example, the court would have to investigate him. In the event that two sets of witnesses expressed opposite opinions on his state of mind, the Gemara concludes that we nullify the sale, leaving the land in the possession of Bar Shatya, as it was in the beginning.