5.23 An operation is that which must happen to a proposition in order to make another out of it.
Black (p. 259): “W. wishes to make a distinction between an operation and a function (5.251), yet the difference between the two seems at first nothing more substantial than a difference in point of view (and consequently in terminology). Mathematicians commonly use the terms ‘function’ and ‘operation’ interchangeably.”
Black (p. 260): “The important point is that W. restricts ‘operation’ to the case where the ‘bases’ and the ‘result’ (5.22) of the operation are internally related.”