The limits of my language mean the limits of my world.

This remark provides a key to the question, to what extent solipsism is a truth. In fact what solipsism means, is quite correct, only it cannot be said, but it shows itself.

The world and life are one.

The thinking, presenting subject; there is no such thing.

The subject does not belong to the world but it is a limit of the world.

Here we see that solipsism strictly carried out coincides with pure realism. The I in solipsism shrinks to an extensionless point and there remains the reality co-ordinated with it.

The I occurs in philosophy through the fact that the “world is my world”.

For an answer which cannot be expressed the question too cannot be expressed. The riddle does not exist.

Whereof one cannot speak, thereof one must be silent.

Ludwig Wittgenstein – Tractatus Logico-Philosophicus

Brain in a Vat

Thought experiment: the brain is closed in the dish and stimulated by an apparatus connected to receive stimuli. This apparatus (or scientist through it) creates a perfectly coherent illusion of the existence of persons, objects of everyday experience (however, all experiences are actually the result of electrical impulses sent by the computer). You can go ahead and assume that all people (all sensory organisms) are the brains (nervous systems) in the vessels connected to the system that generates a collective hallucination.

Hilary Putnam

In Captivity of Habits

Pure experience informs us about permanent sequences of facts; but does not tell us that one fact results from the other. If you pull the trigger of a shotgun, you will hear a shot; but what we really find is that there has been a shot after pulling the trigger, not that it arose from, not that was its effect. How it happens, that one fact follows the other, is not given by the experience; so if we have to stick closely to the experience, we must renounce causal connections, and be content with just setting permanent sequences. It was the most unexpected and unique thesis by Hume.

There is, therefore, no basis to recognize causal relationships as necessary: ​​neither rational, nor experiential. And yet in life and in science we always recognize them, and we expect that when the cause happened, inevitably too the effect will happen. Such attitude of mind requires explanation; it was, in turn, a new issue for Hume: why, although we have no basis for this, we recognize the existence of causal relationships?

We do this because we rely on previously gathered experience and we move this experience ahead. So far, after pulling the trigger of a shotgun, the shot fell, so we think it will continue to be the same. But in doing so, we no longer stay within the limits of pure experience, but we cross them. These two sentences are by no means equivalent: “I found that this object here is accompanied by such a result” and “I expect that other objects, which, as far as we know them, are similar to that, will be accompanied by similar effects.” From one of these sentences to the other we would go only through reasoning, but is there such reasoning? Do we have the right to extend into the future our previously gathered experience?

There is no reasoning, which entitles to extend the existing experience into the future. There is no contradiction in the assumption that although certain event had some result, a similar event will have a different result. Moving the experience to the future is not done by reasoning, but by a factor of a different kind altogether; the conclusions from cause to effect are not a matter of reasoning. These are the matter of habit.

Constant repetition of certain relations changes nothing in the nature of these relations, but changes our attitude towards them. In the mind, it produces the tendency to expect further repetitions. Since we are used that after pulling the trigger, a shot falls, we think it will continue to be so. But the basis for this conclusion is purely subjective. Although this inclination has a certain objective basis, namely regularity in the occurrence of the relations previously observed; but precisely this basis alone is insufficient to draw conclusions. The actual basis for the conclusion is not objective, but subjective, and it is emotional, not conceptual. The inference here is an act of faith, not the act of knowledge.

The sense of necessity is not the basis for our conclusions, but their outcome; the greater it is, the more conclusions we have drawn. The search for causal conclusions is the instinct that nature has given us. It gave us the instinct without giving the understanding. We conclude about future things without knowing the basis of our conclusions, just as we can move without the knowledge of muscles. But instinct is not knowledge.

Wladyslaw Tatarkiewicz – History of Philosophy Volume II Modern Philosophy until 1830.