Peirce used the term "abduction" ambiguously for at least four different concepts throughout his working life. He only became aware of the full significance of this in his later years, for which he apologized profusely. One of his later uses of "abduction" was for the invention of abstract theory to explain the generals of nature and life. Peirce called this "reasoning to the best explanation of the phenomena." This is the meaning of "abduction" that the semiotic paradigm focuses on.