A major focus of Orality and Literacy is the effects of literacy on society and on the mind of the individual. Ong states that writing is a technology, but one which has had an unparalleled impact on human cognition and on the structure and functioning of global society.

In Chapter 4, Ong discusses the progressive changes wrought on cognition and society by the introduction, proliferation, and internalization of literacy. The main cognitive effects of literacy stem from the fact that literacy essentially frees the mind from the mnemonic load of retaining and recalling conventional knowledge. Cognition is no longer restrained by a reliance on formulaic, easily memorable thought patterns, and so thoughts can become more abstract and innovative. Literacy also allows for and conditions more analytic thought patterns, leading to the deconstruction of preestablished norms and the ability to study all manner of fields and phenomena. Ong credits the unprecedented literacy of ancient Greek civilization with the blossoming of modern analytical philosophy and science.

Ong describes the differences between a primary oral society and the type of literate society with which his readers are familiar, although he does note that such differences are not solely due to the effects of said literacy, but also due to contemporaneous political, social, and technological advancements.