McLuhan used the approaches of Richards, William Empson, and Harold Innis as an "entrée to the study of media". However, it took many years of work before he was able to successfully fulfill their approaches. McLuhan determined that "if words were ambiguous and best studied not in terms of their 'content' but in terms of their effects in a given context and if the effects were often subliminal, the same might be true of other human artifacts, the wheel, the printing press, the telegraph and the TV". This led to the emergence of his ideas on media ecology.