[Avodah] Polygamy

[Joseph Kaplan]

RMYG asks about fathers-in-law and daughters-in-law "Are Chazal  
saying that the underlying human nature
is absolute? It might appear that the FIL and DIL get along, but  
there is some predisposition to argument that will always remain? Or  
do we say that even though in this situation the two are best  
friends, Lo Plug?"  And RJR comments "yes and  the interesting  
question (a la R'YBS) is when were they making sociological  
observations subject to change and when were they stating ontological  
truths?"  Assuming, as RMYG does, that RJR is referring to Tav  
L'Meisiv Tan Du, it seems to me that one cannot compare RYBS's  
analysis of Chazal's view of a woman's desire to marry (which, he  
argues, is an ontological and not sociological, observation)  to  
other situations (e.g., FIL and DIL) because RYBS's analysis (which I  
still don't really understand) is based on a pasuk in Beraishit.  I  
don't recall any pesukim about the relationship of FIL and DIL.   
Thus, the question that I have is, if I am correct, it would seem  
that Chazal were making a sociological observation to which, in their  
time, lo plug would apply.  But what if that observation is not true  
any longer; i.e., that today FIL and DIL usually have a very good  
relationship.  (I'm not saying that's true, but it could be so let's  
assume it for purposes of my question.)  In that situation, what  
would the halacha be?

Joseph Kaplan