# I thought there was a difference, but I cannot reproduce it now.   

MC_reminder <- function(first="hello", second="world") {

  return(list(
       index.outside.char= as.character( match.call() ) [[2]]
     , index.inside.char = as.character( match.call()   [[2]]  )
    ))
}
someVar <- "ehrelre"
someVar2 <- "dfsdfsd"

MC_reminder(someVar, someVar2)
MC_reminder(first=someVar, second=someVar2)
MC_reminder(first="newFirst")
MC_reminder(second="justSecond")