|   grammatical? 
 a sentence:
 His reign was much shorter than the reigns of both his father and his son.
 
 to rewrite it:
 
 His reign was much shorter than the reign of his father.
 
 so, usually I write it :
 
 His reign was much shorter than that of his father.
 
 the following sentence is also acceptable:
 
 Their reigns were much shorter than those of their ancestors.
 
 in these cases, THAT agrees with REIGN, and THOSE with REIGNS.
 
 a question comes:
 
 can the first sentence be written as
 
 His reign was much shorter than those of both his father and his son.  ?
 
 it is of course understandable, but the original form seems to be [than those reign of ], without an s, which is absolutely ungrammatical. what do yo think?
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