Marshall McLuhan defined media as anything requiring use of the human body. Under this definition, both computers and clothing can be identified as media. When a media is introduced it is adapted to human senses so that it becomes an extension of the individual, and its capabilities influence the whole of society, leading to change. McLuhan states that there are three inventions that transformed the world: the phonetic alphabet, by virtue of its ability to make speech visible, which McLuhan argues gave rise to the discipline of rhetoric in ancient time and to the study of language and poetics, which was also known as grammar. The printing press in the nineteenth century and the telegraph led to both the modern newspaper and also to journalism as an academic pursuit. The introduction of broadcasting in the form of radio, following on the heels of mass circulation newspapers, magazines, as well as the movies, resulted in the study of mass communication. Due to these technologies, the world was taken from one era into the next. In order to understand the effects of symbolic environment, McLuhan splits history into four periods: the Tribal Age, the Literacy Age, the Print Age, and the Electronic Age.