Idem sonans is something I have put a lot of thought into.  It is something that has become much more complicated with the "advanced technology".  The old book indexes naturally grouped like-sounding names together.  However, the computer is far too literal to do that.

In the computer index, the examiner has to anticipate the various misspellings.  With some names that is tough to do.  Even if they sound alike, they could be spelled very differently and it would be easy to miss today.

The idem sonans rule made more sense when it was likely that examiner would have come across the variation in spelling while searching the index.  Now... well... it's just a dangerous trap.

See "'Idem Sonans' and Good Computer Searching Techniques". 

Best,
Robert A. Franco
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