Uncertainty as to whether an oath was sworn in the first place – such as being uncertain as to whether the oath was sworn, or whether it was sworn and broken – in this case, nothing is required of the one who is uncertain, because the basic principle [and what is certain] is that one is under no obligation, and certainty cannot be dispelled by uncertainty. An oath does not become binding merely by thinking about it; rather it is essential that it be spoken out loud.