Heir versus Descendant of Slytherin

[fanofminerva]

No: HPFGUIDX 98978

Tom Riddle is the /Heir/ of Slytherin.  Being an heir is more than 
being a descendant.  An heir, by definition, is "one who inherits or 
is entitled to inherit another's property, title, etc." whereas a 
descendant is "an offspring of a certain anscestor, family, group" 
(Webster's New World Dictionary).  Being an heir implies being 
designated as such by the person bequeathing the property, etc.  
This is especially true in Tom's case.  Otherwise, any descendant of 
Slytherin would have been able to open the Chamber, control the 
Basilisk, etc.  What is it about Tom Marvolo Riddle that made him 
the HEIR, not just the descendant?  His maternal anscestory was full 
of descendants of Slytherin, but Tom is the heir.  Why?  Do we know 
yet? 

Julie