How can we say a woman who goes abroad likely had a child since Rov women have children. While the majority of women overall have children, I doubt 50% of women are pregnant at any one time. So if the woman goes abroad for one year, the odds are probably less than 50% she would become pregnant. Rov does not seem to work here. Please clarify.
Thank you.
This is a complicated issue and requires some introductions. In general, Rov fall into two basic categories, Ruba d'Issa Kaman, or a Rov which is based on pure numbers, where we know that there are more of one type than the other; and Ruba d'Laisa Kaman, which is a general rule not based merely upon numbers, rather on natural tendencies or human nature.
The dynamics of Rov are not purely statistical, especially the latter type, for statistics can always be rearranged. For example, if we say that most drivers defy traffic laws, this may be true only for drivers under age fifty, or only male drivers, or left-handed drivers, or red-headed drivers etc. In modern statistical studies we use the test group to determine the reliability of the statistic. This method is still not fool-proof for the permutations of the classifications are endless. However, the more specific the group the more reliable the statistic.
On the other hand, Rov, is not merely a gauge of probability, rather a Din that we are beholden to follow the outcome of the Rov when we are in doubt. (Although in general the outcome of the Rov is more probable, it is not due to this probability that we follow the Rov). Therefore, the guidelines which we use to determine the grouping are not based merely on statistical considerations, rather Chazal determined the grouping, and we are then beholden to follow the Rov.
In general, most women have children. Of course, statistically, we could subgroup this generality, into time periods, fertility, etc. However, since we cannot form each subgroup on our own , rather we follow the groupings of Chazal, following the Rov may cause a statistical anomaly which does not contradict the Halacha of Acharei Rabim l'Hatos. In the end of the first Perek of Kesuvos we will gain more insight into how Chazal determined their groupings.
Dov Zupnik
Let me add two points:
1. Bear in mind that we are discussing specifically women in their childearing years, who have no known gynelogical problems. Otherwise, the Rov would clearly not apply
2. We are discussing a man who is childless who is traveling with his wife. In fact, he is towards the end of his life (whether he knows it or not), and probably is desperate to have an heir. I wonder whether the same Chazakah would apply if he had children already -- I doubt it.
In fact, the Gemara may mean to say just that: Most women become pregnant (and eventually bear children, as opposed to stillborns) to their husbands at least once during his lifetime.
-Mordecai Kornfeld
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