    ‘Sentence 1: The answer has nothing to do with  ‘their. cause, however, but with the simple fact  that dictionaries. are ‘not. exercises’ in | bi-  unique substitutability; in other words; if one  of the senses of rin is “operate'.(as in. She.  runs.an engine factory ), that does not make  it valid ‘to assume.that one :can' substitute  operate for run in We ruit.in: the marathon  every year .:Although recognizing this. asa  shortcoming of-dictionaries. and assigning it  arbitrarily to what, for lack-of a better term,  we might call the genius ‘of the language,  ‘might:seem trivial to the casual observer, it is  a valid. matter for concern-in the: realm. of.  lexicology.