The first couple of mishnayos in chapter nine of Y'vamos list classes of women, each of whom is permitted to marry her first husband but forbidden to marry his brother on his childless death, or vice versa, or forbidden to marry either, or permitted to marry both. The lists contain the following classes of woman:
- האלמנה, the widow
- כשרה, (in this context, roughly) someone allowed to marry a kohen
- חללה, (roughly) someone not allowed to marry a kohen
- בת ישראל, (in this context, roughly) someone who is not a mamzeres or convert
- ממזרת, a mamzeres
Why is the first of those definite ("the") and the rest not?