"All propositions are of equal value" (6.4): everything in the world is accidental (only logic is necessary), and so nothing in the world can have transcendent value. If something has value or meaning, that value or meaning must lie outside the world (6.41). Even if there is value or meaning, we cannot talk about it, because it lies outside the world and hence outside the realm of what can be said.
Ethics and aesthetics (which Wittgenstein takes to be equivalent) cannot be put into words, because they make judgments of value (6.421). Actions are not good or bad because of their consequences, but because of the overall attitude toward life that they embody. While the exercise of the will has no direct effect on the world itself, this exercise of the will defines the kind of world a person inhabits: "The world of the happy man is a different one from that of the unhappy man" (6.43).
Death is not an event in life, but is the end of life. My death is not a part of my world or my experience. Effectively, the world comes to an end at the time of death. Wittgenstein remarks: "If we take eternity to mean not infinite temporal duration but timelessness, then eternal life belongs to those who live in the present. Our life has no end in just the way in which our visual field has no limits" (6.4311). Being immortal or having a soul that survives death solves nothing (6.4312): it just serves to extend the limits of our life and our world, but it does not help us to transcend them.
Wittgenstein defines "the mystical" as "feeling the world as a limited whole" (6.45). There is not a mystical understanding that connects us with the nature of goodness or the human soul, but simply an awareness that these things lie outside the world and we cannot contemplate them. The awareness of the ineffability of those things that we feel most compelled to understand is what is mystical.
Questions can only be answered when the questions themselves can be framed in words. Thus, we can only ask questions and get answers regarding facts about the world, and not about anything transcendent. "We feel that even when all possible scientific questions have been answered, the problems of life remain completely untouched. Of course there are then no questions left, and this itself is the answer" (6.52). The essence of the world, if it can so be called, is outside the realm of human discourse and thought.
Wittgenstein concludes that the only correct method in philosophy is to confine oneself to what can be spoken, and, whenever others try to say the unsayable (ethics, aesthetics, metaphysics, etc.), to point out to them that they are speaking nonsense (6.53). He then acknowledges that all the propositions of the Tractatus are themselves nonsensical, and that they are to be used, only as steps, "to climb up beyond them." He famously remarks that the reader must "throw away the ladder after he has climbed up it" (6.54).
Having dismissed the possibility of speaking about traditional philosophical problems, and having dismissed even his own propositions as nonsense, Wittgenstein concludes: "What we cannot speak about we must pass over in silence" (7).
Wittgenstein's discussing of ethics, death, and "the mystical" all center around the idea that there is no position outside the world from which we can look at or talk about the world. For Wittgenstein, ethics is not a part of life; ethics pervades all of life: no aspect of life is untouched by ethics. Our attitude toward the world shapes the world we live in, and it is this general shape of the world—and not a set of maxims like "it's wrong to steal"—that constitutes ethics. Thus, we cannot talk about ethics because we would be speaking about life generally, and we would have to be able to "look at life from the outside" in order to speak about it generally. The desire for immortality similarly seeks some external perspective that gets us beyond the limits of life itself. The feeling of "the mystical," then, is the awareness that this life is all there is, that it is limited, but that there is no position outside of it that we can aspire to.
The concluding remarks of the Tractatus are by far the most controversial. How are we to understand the Tractatus in light of Wittgenstein's claim that what he has said is nonsense? In his introduction, Russell voices the understandable sentiment that "after all, Mr. Wittgenstein manages to say a good deal about what cannot be said, thus suggesting to the sceptical reader that possibly there may be some loophole" (xxi).
The traditional interpretation, perhaps best represented by P. M. S. Hacker, takes Wittgenstein to be pointing out that the kinds of subject matter he treats of lies outside the realm of sensible discourse. Propositions such as "the world is all that is the case" or "the world is the totality of facts, not of things" are nonsense, because they say things about the world as a whole when all we can talk about are itemized facts within the world. The Tractatus treats of things that cannot be said, but can only be shown.
Wittgenstein says explicitly what can only be shown so that we can understand this distinction between saying and showing and will no longer be tempted by metaphysics. The Tractatus is meant to purge philosophy of nonsense talk so that, after we have read it, we can approach philosophy with a recognition that there are certain, unutterable, fundamental truths about the world that can only make themselves manifest.
The rival interpretation, first expressed by Cora Diamond, takes a sterner stance toward what Wittgenstein means when he says that the propositions of the Tractatus are nonsense. If these propositions are nonsense, that doesn't mean that they technically can't be spoken, but they point toward deep, underlying, and unsayable truths about the nature of the universe. If these propositions are nonsense then they are plain nonsense, just as much as "the number two is purple" or "gurgle cluck ping" are nonsense. According to Diamond, Wittgenstein is dismissing the metaphysics of the Tractatus as an unsayable truth.
Surely, we can make some sense of the propositions of the Tractatus, so how can we say they are as nonsensical as "gurgle cluck ping"? They are nonsense, Diamond suggests, in that we cannot construct a proposition with a sense of the form "Wittgenstein says that p," where p is one of the propositions in the Tractatus. None of these propositions have a correct logical form, so they cannot be considered a sensible part of rational discourse.
This is not to say that we cannot think we understand them. Diamond emphasizes that, at 6.54, Wittgenstein does not say, "My propositions serve as elucidations in the following way: anyone who understands them eventually recognizes them as nonsensical." Rather, he says, "anyone who understands me." There is nothing in the propositions that can be understood. However, we can try to understand the frame of mind that would be necessary to think that these propositions make sense. According to Diamond, Wittgenstein is asking his readers to appreciate the frame of mind that produces metaphysical claims of the sort that we find in the Tractatus so that they can then appreciate why such claims are nonsensical.
Hacker takes Wittgenstein to believe that objects, states of affairs, and all the rest exist, but that we cannot talk about them. Diamond takes Wittgenstein to be denying that it even makes sense to think of there being objects, states of affairs, and so on. Diamond's radical re-reading suggests that the Wittgenstein of the Tractatus shares with the Wittgenstein of the Philosophical Investigations the feeling that even to entertain metaphysical notions is deeply misguided.
Diamond's interpretation is very bold, and presents us with a far more consistent reading of the closing passages of the Tractatus. However, it does leave many hurdles in interpreting the rest of the book. How can we even make use of Wittgenstein's distinction between sense and nonsense if the propositions in which he lays out this distinction are themselves nonsensical? How are we to understand Wittgenstein's later rejection of logical atomism if that was never a position he held to seriously? Opinion is mixed as to whether the Diamond interpretation adequately answers these questions. The New Wittgenstein contains a number of good essays on the topic, as well as a reply from Hacker.