Ketubot 18: Signing Your Life Away

What happens when two parties have a monetary claim? What level of responsibility is expected for one to be able to stake a legitimate claim? Why does the Gemara talk about a katan, a minor, bit who is clearly past the age of majority? Also, on witnesses - where they claim the signed under duress, then? What does it mean to be compelled to sign sworn testimony? When does testimony line up with this, or does ? || Talmudic Principles: Modeh ba-miktzat. No self-incrimination.