In the years 1891–1892, Frege gave more thought to the philosophy of language that would help ground his philosophy of mathematics. He published three of his most well-known papers, ‘Function and Concept’ (1891), ‘On Sense and Reference’ (1892a), and ‘On Concept and Object’ (1892b) in this period.  These works were eventually supplemented by three other papers on the philosophy of language, from a later period, ‘The Thought’ (1918a), ‘Negation’ (1918b), and ‘Compound Thoughts’ (1923).  As we shall see in Section 3.3 below, these works have to be considered in light of recent scholarship providing evidence that Frege heavily borrowed from Stoic philosophy.  Though Frege always motivated and recast (often in rigorous terms) ideas that he absorbed from others, the documentation concerning the origins of many of his ideas in the Stoic corpus has to be taken seriously.