What does Frege mean when he says that a proposition or a sentence has a determinate sense? How did he come to this conception, and did his views change during his philosophical career? How do his views on these matters relate to what we take ourselves to mean when we say that something makes sense? These are the questions which will guide this examination of “determinacy of sense” in Frege. My investigation will take a historical shape, for I hope to trace the process of argument and philosophical enquiry by which Frege came to the view of determinate sense close to the heart of his logicism. I will try to show how his approach to the problems of language allowed metaphysics to steal, unnoticed, into his theoretical vision of language, in particular with regards to his account of what it is for a linguistic expression to make sense, or ‘have a sense’. The full account of why and in what way his theory is metaphysical will be left to the last section, where I turn to sections of the Investigations that are directed specifically at Frege’s thoughts.