The “truth of solipsism” if it could be stated (and it cannot be) would have to be stated “from the outside of one’s own consciousness ,” but nobody can get outside his or her immediate experience (i.e., his or her consciousness); it has no outside. So we are unable to say what we try to say with expressions such as “My world is all the world there is,” or “I never have anybody else’s experience but my own.” (The fact that we speak of “losing” and “regaining” consciousness and of states of “half’ consciousness and “heightened” consciousness, quite unconcerned about whether it is our own or someone else’s, does not bear on these questions of perception or consciousness-of.)
What is, however, inextricably tied up with first-person experience is the present moment. In a sense all experience is experience within the present moment (even if it involves memory or imagination or future anticipations). As Wittgenstein pointed out, however, language takes place in time, and before the end of the sentence is reached, immediacy is gone or replaced by a new immediacy. All the difficulties that attach to the solipsistic situation of the first person (that is, I) appear again in connection with the unique status of the present moment. The present appears to be incommensurably real, while no such claim can be made for the past and the future. It is even confusing to say that the present is fleeting, for there is a sense in which it doesn’t seem to belong to time at all, the sense in which it is, by contrast with past and future, real, however short-lasting that reality. 
(It should be noted that this is another place where the orbits of Heidegger and Wittgenstein approach each other, for Heidegger also was centrally concerned with the “mystery of presencing” and finally seemed to identify Being with presencing.
The topic of solipsism is discussed at great length in the Blue Book (1933-34), pp. 44-74 and the topic of the present in Philosophical Remarks (1929-30), pp. 80-88. Perhaps the most illuminating discussion of all is in “Notes for Lectures on ‘Private Experience’ and ‘Sense Data’”, reprinted in Philosophical Occasions 1912-1951 (1934-36).
The importance of this topic cannot be exaggerated because it has a close connection to Wittgenstein’s thinking about the subject and the self, and later on what he has to say about mental processes and the impossibility of a metaphysically private language. All of this comes under the heading of one of the most far-reaching changes carried out by Wittgenstein’s philosophy: the emptying-out of the “inner world” as the main locus of the most valuable kind of experience, not in the interests of a reductionist behaviorism (though Wittgenstein is often at first misunderstood in this way), but of a much more integrated soul-and-body and body-and-world.
The initial step in this direction was his attempt to “show the fly the way out of the fly-bottle,” as he put it, which meant to release the solipsistic subject (the totally private subject of modern Cartesianism and Calvinist capitalism) from the trap in the human being. This lonely, isolated, fearful subject has been at the center of Western philosophy since the time of Descartes as, in a sense, the balance to the objectified mathematical universe. Wittgenstein’s work was to carry this conception to its logical extreme and then to rearrange the entire geography. When we grasp the point that
what the solipsist means is quite correct, only it cannot be said, but makes itself manifest.
The world is my world. . . . (T 5.62)
I am my world. (The microcosm.) (T 5.63)
Then we see thaL the subject, any subject, can be identified by its world and does not need any special “content” of its own, qua subject, which is not and cannot be “world.” At this point Wittgenstein can say, in flat rejection of Descartes (and the whole ego basis of modern philosophy),
There is no such thing as the subject that thinks or entertains ideas. (T 5.631)
Here it can be seen that solipsism, when its implications are followed out strictly, coincides with pure realism. The self of solipsism shrinks to a point without extension, and there remains the reality coordinated with it. (T 5.64)
The philosophical self is not the human being, not the human body, or the human soul, with which psychology deals, but rather the metaphysical subject, the limit of the world—not a part of it. (T 5.641)
Here, in Zen Buddhist parlance, the goose is out of the bottle, but not totally because the metaphysical point remains, though this can have no personal identity and therefore no attachments, desires, or anguishes. Otherwise the self is gone!
Here too the subjective source or base of thinking disappears. Thinking takes place, but it is not “done” by an agent, or a private locked-away metaphysical self. It is part of the factual world, as are the soul and body, or it is an illusion. Wittgenstein’s no-agent conception of thinking leaves us not with Descartes’s Cogito ergo sum, I think therefore I am, but with Thinking takes place, therefore I am not.
Wittgenstein makes a sharp distinction between thinking, which he says does not need a subject or agent, and willing, for example, moving one’s own body, which does involve agency. If the essential meaning of thinking is picturing, we can begin to see what he has in mind . On the other hand, this doctrine leaves us uneasy. And the uneasiness perhaps turns around Wittgenstein’s own example of thinking.
Wittgenstein’s own philosophical method always seems to have involved an inner questioning and answering (though this was hidden by the ex cathedra pronunciamento style of the Tractatus’), and it is difficult to understand why he did not see at least the inner questioning as an act of will, though his reply might have been that the questions “came to him” too, as much as the answers, and therefore were not, strictly speaking, his doing. But even if this be admitted, it would seem that “directing one’s attention” is, at least to some extent, within one’s own control, and this is part of thinking. We will return to this subject when we look at what he later on had to say about the grammar of the word thinking (which is the correct way to approach this problem).
What is clear enough is that Wittgenstein’s discussion of solipsism (paralleled in sheer unrelenting tenacity only by Samuel Beckett ’s discussion of the related topic of personal identity in The Unnamable) is one of the most profound approaches to the problem of the self to be found in philosophical literature, East or West. We can compare it to the thought of the Buddhist-oriented philosopher, more readable, but also far less profound and far-reaching, Arthur Schopenhauer . As it happens, Schopenhauer was Wittgenstein’s first philosophical reading and may well have been his introduction to the subject of solipsism.
Schopenhauer’s main work, Die Welt as Wille und Vostellung (The World as Will and Idea , 1819), begins with the notorious sentence “The world is my idea.” We all know what he meant, but his philosophical naivete in leaving it at that and in a way building his whole system of thought on that must have left Wittgenstein somewhat aghast. Should not the next sentence have been “Whom are you telling this to then, and how could they (not being you) possibly understand it”? And with these additions the fat is in the fry.
Wittgenstein suggests, perhaps half-humourously and without applying his words to Schopenhauer, that we might be willing to “accept this notation” (i.e., let the philosopher talk that way) and agree that the world is Schopenhauer’s world without being so rude as for each of us to make the same claim for him or herself (which would be to be as absurd as Schopenhauer was). But what would be accomplished by this, except to humor the philosopher? Philosophy is full of such insults to common sense; this is only one of the most outrageous of them.
What makes Wittgenstein a great philosopher is that he really does try to seize the nettle, sting and all, and hang on to it for years, in this case trying to find out what made Schopenhauer say such a thing and how it could be reconciled with common sense. That the problem is ultimately that of the “fly in the fly-bottle,” or releasing the human self from its self-imposed prison, makes it not just a philosophical problem, but also a religious and civilizational one. That Wittgenstein was ultimately successful in solving this we will see in Part II of this book.