a proposition might be e.g. "My body has never disappeared and reappeared again after an interval." Might I not believe that once, without knowing it, perhaps is a state of unconsciousness, I was taken far away from the earth - that other people even know this, but do not mention it to me? But this would not fit into the rest of my convictions at all. Not that I could describe the system of these convictions. Yet my convictions do form a system, a structure. And now if I were to say "It is my unshakeable conviction that etc.", this means in the present case too that I have not consciously arrived at the conviction by following a particular line of thought, but that it is anchored in all my questions and answers, so anchored that I cannot touch it. I am for example also convinced that the sun is not a hole in the vault of heaven. All testing, all confirmation and disconfirmation of a hypothesis takes place already within a system. And this system is not a more or less arbitrary and doubtful point of departure for all our arguments: no, it belongs to the essence of what we call an argument. The system is not so much the point of departure, as the element in which arguments have their life. To be sure there is justification; but justification comes to an end. What does this mean: the truth of a proposition is a certain? With the word "certain" we express complete conviction, the total absence of doubt, and thereby we seek to convince other people. That is subjective certainty. But when is something objectively certain? When a mistake is not possible. But what kind of possibility is that? Mustn't mistake be logically excluded? If I believe that I am sitting in my room when I am not, then I shall not be said to have made a mistake. But what is the essential difference between this case and a mistake? Sure evidence is what we accept as sure, it is evidence that we go by in acting surely, acting without any doubt. What we call "a mistake" plays a quite special part in our language games, and so too does what we regard as certain evidence. It would be nonsense to say that we regard something as sure evidence because it is certainly true. Rather, we must first determine the role of deciding for or against a proposition. The reason why the use of the expression "true or false" has something misleading about it is that it is like saying "it tallies with the facts