A language is a system of signs (indices, icons, symbols) for encoding and decoding information. Since language and languages became an object of study (logos) by the ancient grammarians, the term has had many and different definitions. The English word derives from Latin lingua, "language, tongue," with a reconstructed Proto-Indo-European root of*dnghû-, "tongue," a metaphor based on the use of the physical organ in speech. The ability to use speech originated in remote prehistoric times, as did the language families in use at the beginning of writing. The processes by which they were acquired were for the most part unconscious.