Although in a sense the title is misleading due to its one-sidedness, "On Certainty" has rightly been characterized as a work on epistemology, a work that inaugurates new lines of thought on the concepts of knowledge, doubt, and justification of beliefs. But regardless of its contribution to the articulation of epistemological positions, the book clearly constitutes Wittgenstein's third masterpiece (after the "Tractatus" and the "Philosophical Investigations"), expanding and broadening his reflections on language, logic, and human life.

The richness of observations, the philosophical fertility of questions and different answers, as well as the variety of themes addressed in these notes, not only confirm such a characterization but also allow the reader to follow the course of thought of a great philosopher.

These notes touch on the problems of idealism and skepticism, the concept and role of doubt, the concept of knowledge and its foundation, the concept of justification and the justification of empirical beliefs, as well as many other epistemological issues, beyond the emblematic concept of certainty, which occupies a large part of the philosophical investigations of the book.