Solipsism ( //) is the philosophical idea that only one's own mind is sure to exist. The term comes from the Latin solus (alone) and ipse (self). Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure. The external world and other minds cannot be known, and might not exist outside the mind. As a metaphysical position, solipsism goes further to the conclusion that the world and other minds do not exist. As such it is the only epistemological position that, by its own postulate, is both irrefutable and yet indefensible in the same manner. Although the number of individuals sincerely espousing solipsism has been small, it is not uncommon for one philosopher to accuse another's arguments of entailing solipsism as an unwanted consequence, in a kind of reductio ad absurdum. In the history of philosophy, solipsism has served as a skeptical hypothesis.
Wahrnehmung ist Falschnehmung
The earth is as old as we are, no older. How could it be older? Nothing exists except through human consciousness. Before man there was nothing. After man, if he could come to an end, there would be nothing. Outside man there is nothing.
O'Brian (George Orwell in 1984)
First published Wed Nov 22, 2000; substantive revision Fri Mar 26, 2010
One of Brentano's foremost aims in philosophy was to provide a new foundation for epistemology and logic as two closely related disciplines. He tried to achieve this by a systematic analysis of the mental phenomena involved in attaining knowledge and in drawing inferences. For Brentano knowledge is reached by judgements that are directly or indirectly evident, and logical inferences can contribute to our knowledge because they can make a judgement indirectly evident for us. Hence both epistemology and logic rely on a conception of judgements, how they differ from other mental phenomena, and how they are related to each other.
Brentano's view of the nature of judgement differs significantly from other views that can be found in Aristotle, Kant, or Frege. In contrast to Aristotle, Brentano emphasizes the importance of existential judgements with only one term, and claims that predicative judgements are a special case of existential ones. In contrast to Kant, he emphasizes the difference between presentations and judgements, rejecting their unification in the single category “thinking”. In contrast to Frege, he holds that judgements do not require the existence of complete thoughts or propositions which have to be grasped before a judgement can be made. It is the mental act of judging, not its object or content, which is the bearer of truth-values. In view of these differences Brentano's theory of judgement has been called existential (non-predicative), idiogenetic (non-reductionist), and reistic (non-propositional).
Today Brentano's theory does not have many adherents. The now dominant view is that propositions or sentences are the objects of belief, and that judgements occur when beliefs are acquired, manifested, or changed. Logical inferences are then defined as relations between propositions or sentences, abstracting from the mental attitudes that go along with them. Although this anti-psychological approach is widely accepted today, there is still an open question concerning the order of explanation here: Are beliefs and judgements true because they are directed at true propositions, or should we say that propositions (and sentences) are true because they express true beliefs and judgements? Once this question is raised, Brentano's theory of judgement remains an interesting alternative to the current mainstream in logic and epistemology.