Is there a rule to know whether the locative form of a masculine noun ends in «е» or «у»? For example, «мозг» vs «город»
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Is there a rule to know whether the locative form of a masculine noun ends in «е» or «у»? For example, «мозг» vs «город»
отnewNEWS
Янв 19, 2023 
вопрос, который меня ставит в тупик
в моём мозге выросла стена… дождёмся профессионалов филологов
I can’t advice on overall rule but there is a slight difference for Мозг.
«в мозге» means something happening inside brain as an organ, aka physical biological process
«В мозгу» used as «in mind», mentality and psychology matters.
Maybe you meant case endings? Cause in «В его мозгу», and, for example «В городе» there are different cases.