Philosophical Investigations (Philosophische Untersuchungen) is a highly influential work by the 20th-century philosopher Ludwig Wittgenstein. In it, Wittgenstein discusses numerous problems and puzzles in the fields of semantics, logic, philosophy of mathematics, philosophy of psychology, philosophy of action, and the philosophy of mind. He puts forth the view that conceptual confusions surrounding language use are at the root of most philosophical problems, contradicting or discarding much of that which was argued in his earlier work, the Tractatus Logico-Philosophicus.
- 114. If you are not certain of any fact, you cannot be certain of the meaning of your words either.
- 115. If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.
- 126. I am not more certain of the meaning of my words that I am of certain judgments. Can I doubt that this colour is called "blue"? (My) doubts form a system.
- 158. Can I be making a mistake, for example, in thinking that the words of which this sentence is composed are English words whose meaning I know?
- 160. The child learns by believing the adult. Doubt comes after belief.
- 163 ..... For whenever we test anything, we are already presupposing something that is not tested. ......Does anyone ever test whether this table remains in existence when no one is paying attention to it? We check the story of Napoleon, but not whether all the reports about him are based on sense- deception, forgery and the like. For whenever we test anything, we are already presupposing something that is not tested. Now am I to say that the experiment which perhaps I make in order to test the truth of a proposition presupposes the truth of the proposition that the apparatus I believe I see is really there (and the like)?
- 174. I act with complete certainty. But this certainty is my own.
109. "An empirical proposition can be tested" (we say). But how? and through what?
110. What counts as its test? - "But is this an adequate test? And, if so, must it not be recognizable as such in logic?" - As if giving grounds did not come to an end sometime. But the end is not an ungrounded presupposition: it is an ungrounded way of acting.
A reaction: If you could be wrong about everything, you cannot be certain of the meaning of your words either and cannot make knowledge claims. Knowledge claims and judgments cannot transcend the certainty about my words and presupposes something that is not testable. Not being certain about anything is self-refuting because I possess the certainty of the doubt.