In this book I want to make different syntheses of Coserius theory convinced that his theory is not only a theory about language but the philosophy of someone who focused his life on that aspect he considered the radical reality of what to be a human subject is. For Coseriu, to be a man, that is, to be a human subject, is to be someone determined by speaking. A man is el ser hablante, the speaking subject. His instrument to devise and develop his theory is determining, an intellective instrument for interpreting the exclusive and excluding fact of the human activity of speaking. For Coseriu, the study of language must be based on el saber originario, the competence human subjects have before speaking, the knowledge they have for interpreting their reality as human subjects living in the world they created in participation and collaboration with others in history. His theory thus is hermeneutics, the interpretation of the human life in the period of history they live. Language thus constitutes the defining fact of humans.