Ludwig Josef Johann Wittgenstein (1889 - 1951) was an Austrian-British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. The 'Tractatus Logico-Philosophicus' (Logical Philosophical Treatise or Treatise on Logic and Philosophy) is the only full-length philosophical book by the Austrian philosopher Ludwig Wittgenstein which was published during his lifetime. The goal of the work is to identify the relationship between language and reality and to define the limits of science. He famously summarized the book in the following way: 'What can be said at all can be said clearly; and what we cannot talk about we must pass over in silence.'