Tractatus Logico-Philosophicus opposes Frege and Russell’s universalist conception of logic. In the universalist view, logic is the supremely general set of laws, the foundation on which the edifice of knowledge is built. Wittgenstein, by contrast, argues that logic is not a set of laws at all. Logic is not distinct from the sciences simply by virtue of being more general but by virtue of being something entirely different altogether from the sciences.

According to Wittgenstein, logic has no laws, and there are no logical objects or relations. The assumption that there must be laws, objects, and relations is a holdover from the assumption that logic is like the sciences, only more general. Laws, objects, and relations are the content of a body of knowledge, and according to Wittgenstein, logic is all form and no content. If the universalist conception sees logic as the foundation on which the edifice of knowledge is built, Wittgenstein sees logic as the metallic framework around which the edifice is structured. Logic itself says nothing, but it determines the form and structure of everything that can be spoken about.

Relying on the say–show distinction, Tractatus Logico-Philosophicus draws strict limits to what can be said intelligibly. Wittgenstein limits the sayable to empirical propositions: language is suited to describing facts in the world. By contrast, we cannot say anything that speaks about the world as a whole, that speaks about value, or that purports to speak from a perspective outside the world. Consequently, metaphysics, ethics, aesthetics, and most of philosophy goes out the window.

Wittgenstein does not claim that these things are useless, simply that language is unsuited to dealing with them. For instance, the attitude we hold toward the world and the way we go about living expresses our ethical worldview. Wittgenstein criticizes the notion that this worldview can be put into words in the form of ethical maxims or laws and still remain meaningful. For him, our ethical worldview can only be shown and cannot be said. In asserting that most of what we consider philosophy lies beyond the limits of what can be said, Wittgenstein reconceives the role of philosophy. Philosophy should stand as a watchdog at the limits of what can be said and correct those who try to say the unsayable.

The final few self-refuting propositions of Tractatus Logico-Philosophicus are the subject of great scholarly controversy. What should we make of Wittgenstein’s claim that all the propositions in Tractatus Logico-Philosophicus are nonsense?

One school of thought takes Tractatus Logico-Philosophicus to be the last word in nonsense, so to speak. According to this interpretation, the propositions of Tractatus Logico-Philosophicus are nonsense, strictly speaking, but it is only by understanding them that we can recognize that they are nonsense. Although they are nonsense, the propositions of Tractatus Logico-Philosophicus point to deeper truths, and once we have recognized these deeper truths we can reject Tractatus Logico-Philosophicus along with all the other nonsense that makes up philosophy.

An alternative school of thought rejects this previous interpretation as being too soft. If the propositions of Tractatus Logico-Philosophicus are nonsense, then they are nonsense, and that is all there is to it. The important thing, according to this second interpretation, is to grasp the frame of mind that would think that these propositions make sense and, by grasping it, to recognize the inconsistency of this frame of mind. According to this view, the propositions of Tractatus Logico-Philosophicus do not point to deeper truths. There are no deeper truths, and we can only appreciate this once we have grasped that the propositions of Tractatus Logico-Philosophicus are nonsense.