 Central to Frege’s legacy for discussions of mental or intentional content has been his distinction between sense (Sinn) and reference (Bedeutung), and his use of this distinction to cope with the apparent failures of substitutivity of (ordinarily) co-referential expressions in contexts created by psychological verbs, of the sort mentioned in Section 2. In Frege’s famous example: you may understand the expressions “The Morning Star” and “The Evening Star” and use them to refer to what is one and the same object—the planet Venus. But this is not sufficient for you to know that the Morning Star is identical with the Evening Star. For the ways in which an object (the “reference”) is “given” to your mind when you employ these expressions (the senses or Sinne you grasp when you use them) may differ in such a manner that ignorance of astronomy would prevent your realizing that they are but two ways in which the same object can be given.