Brother-in-Law, Sister-in-Law

These are the only really tricky in-law terms. “Brother-in-law” and “sister-in-law” each have two or three meanings. All authorities agree on the first two meanings, but there is some controversy about the third (and I personally don’t accept it).

My sister-in-law could be:

1. the sister of my spouse, or
2. the wife of my brother, or
3. the wife of my spouse’s brother. (This meaning is accepted by The American Heritage Dictionary of the English Language (Third Edition, 1992), but not by all authorities.)

Similarly, my brother-in-law could be

1. the brother of my spouse, or
2. the husband of my sister, or
3. the husband of my spouse’s sister. (This meaning is accepted by The American Heritage Dictionary of the English Language (Third Edition, 1992), but not by all authorities.)

Consider the following example: Al marries Betty; Betty has a sister Bonnie, who marries Calvin.

         Harry = Sally                                |                                      +                             --------------------                   |                  |             Al = Betty            Bonnie = Calvin 

The siblings-in-law:

• Al is Bonnie’s brother-in-law (definition 2), and Bonnie is Al’s sister-in-law (definition 1);
• Betty is Calvin’s sister-in-law (definition 1), and Calvin is Betty’s brother-in-law (definition 2).

So much is agreed. The question is, are Al and Calvin brothers-in-law (definition 3)? Someone once wrote to Ann Landers, the advice columnist, describing this situation. Ann replied: “You are no relation; you are just two men who married sisters.” Though I agree with Ann on this one, I admit that it’s awkward for Al to refer to Calvin as “my wife’s brother-in-law” or “my sister-in-law’s husband”. Probably that’s why Al might refer to Calvin as “my brother-in-law”.