Theme 1: Theory of science

• What does Russell mean by "sense data" and why does he introduce this notion?

All objects that we perceive to exist in our world can be perceived in numerous different ways. An objects color, size, proportions and constraints may differ from mind to mind and also differ depending on what kind of light that's illuminating the object, from which angle and which distance the individual is watching it. The touch of an object isn't the same when touched with different body parts. The noise an object makes isn't necessarily the same from every point of the object. Russell introduce the term sense-data as a way to describe this momentary sensation of an object, and he uses it to differentiate between how different minds perceive an object under certain circumstances and the actual physical object itself and if the object actually exists. The sense-data isn't the physical object and you can't say it is actual attributes of the physical object, it is merely how it is perceived, the immediate experience that can differ in so many ways.

• What is the meaning of the terms "proposition" and "statement of fact"? How does propositions and statement of facts differ from other kinds of verbal expressions?

A proposition is the description, the explanation, of an object. You can make propositions to describe an object, and there a many ways in which a description can be made. When describing, say a historical person, one cannot actually view the person and obtain sense-data, so one has to rely on propositions made about the person. The propositions does not necessarily have to be true, and they depend heavily on the individual uttering the proposition and that individuals acquaintance to the object in question. A statement of fact is however a description where you make a stand on whether or not a fact is true. Russell means that a statement of fact is something holds a higher value of the truth than the proposition does, and it is based on facts that can eliminate other descriptions of the object.

I interpret that propositions and statements of facts differ from other verbal expressions in the sense that they are descriptions based on acquaintances, the experiences of things.

• In chapter 5 ("Knowledge by Acquaintance and Knowledge by Description") Russell introduces the notion "definite description". What does this notion mean?

Russell talks about both definite descriptions and ambiguous descriptions. The ambiguous description would be a description that could imply a large number things, while the definite description would only refer to one certain object. As an example Russel use the ambiguous description: "a man", which could refer to any number of different men, and he uses the definite description "the man with the iron mask", which only refer to one special man, one object. The definite description is what is 'known by description' - it is the description of what is known of a physical object by the experienced sense-data of it.

• In chapter 13 ("Knowledge, Error and Probable Opinion") and in chapter 14 ("The Limits of Philosophical Knowledge") Russell attacks traditional problems in theory of knowledge (epistemology). What are the main points in Russell's presentation?

Russell doesn't accept that true belief is the same as knowledge. There are premises that can be true, but still not lead to actual knowledge, as with the example Russel makes: "All Greeks are men; Socrates was a man". The premise is true, since Socrates was a Greek and a man, but it's a fallacious process of reasoning. Russell makes the point that all the knowledge we have of truths always contains a certain degree of doubt. Therefore one can question if there can really be any true knowledge of any kind, but merely a belief of true knowledge.