Wittgenstein probably became acquainted with the works of Frege through reading Russell's The Principles of Mathematics, Appendix A of which contains a detailed description of Frege's logical and arithmetical doctrines. But it is also possible that he was referred to the works of Frege by Samuel Alexander, professor of philosophy at Manchester, where Wittgenstein studied aeronautical engineering between 1908 and 1911. Be that as it may, by 1911 he had evidently read Russell's book and Frege's Grundgesetze der Arithmetik carefully, and had become deeply preoccupied with the philosophy of mathematics and logic—sufficiently so to correspond with Jourdain in 1909 on the matter of Russell's paradox of classes. He went to visit Frege in Jena, apparently in the summer of 1911, in order to discuss with him some objections he had to Frege's theories. Frege, as Wittgenstein reminisced to Geach after the Second World War, 'wiped the floor' with him 1 —but also encouragingly invited him to come again, and, more importantly, advised him to go to Cambridge to work with Russell. That fortunate advice set the young Wittgenstein on the path of his lifelong vocation.
Wittgenstein visited Frege again a number of times before the First World War in order to discuss his ideas about the philosophy of logic that were ultimately to grow into the Tractatus. How much Frege understood of Wittgenstein's embryonic ideas is unclear. After a visit in December 1912, Wittgenstein wrote to Russell 'I had a long discussion with Frege about our Theory of Symbolism of which, I think, he roughly understood the general outline. He said he would think the matter over.'