We propose that the discipline or practice of media literacy defined as the ability to access, analyze, evaluate and create media in a variety of forms can be enriched and made more effective by incorporating two of Marshall McLuhan's insights into the nature of media. The first insight is that the effects of media that are independent of their content and intended function are subliminal and they are important because they "shape and control the scale and form of human association and action." The second insight is that the notion of media includes not just communication media but also all forms of human technology, tools and artifacts. We define "mediacy" as the study, understanding and consideration of these two key insights from McLuhan, and that mediacy compliments, and enriches, the traditional media literacy approach.