Theme 1: Theory of Science Pre-reflection

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

Although we might all agree that things exist in reality we most often have a very different experience of them at different times. An object will look, feel and sound differently from different perspectives and at different times. To differentiate between the appearance of an object and the reality or "truth" of an object, Russell introduces sense-data and physical object where the former is the appearance of the latter. In other words sense-data is the immediate knowledge of the object through sensation, our experience of it. The way I understand Russell is that we may infer the physical object from our immediate knowledge as it is created by the physical object. The sense-data is not the truth about the physical object but only the truth about the sense-data itself. Therefore, our sensation, according to Russell, is only of the physical object's appearance and not the object itself. Also, Russell also states that sense-data is personal. Our sensations and experiences cannot be the same as we cannot have the exact same perspective at the exact same time. Our different sensations will however be similar. Russell also states that if only sense-data existed and not the physical objects this would mean that they would disappear as soon as we aren't sensing them and then reappear again when we do sense them. 

–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 a statement about an object. A proposition could be on the form "A is 'so-and-so'" and must be composed of "constituents with which we are acquainted". So if we are acquainted with the man in the iron mask and Alexander Dumas' explanation of who he really is we might put forward the proposition that "Louis XIV's twin brother is the man in the iron mask". We do however not know whether it is true or not. But if it was true, all implications made by this proposition would also be true. A proposition exemplified by Russell is that "two and two are four". Is this a statement of fact? Surely this is true a priori, since the definition of our mathematical axioms require two and two to be four. This makes it a fact inevitably. However these axioms are arbitrary. Two and two might not be four with different axioms. A fact might be a fact in some cases and others not, it all depends on the context. 

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

Russell differentiates between two types of descriptions: ambiguous and definite. An ambiguous description is on the form "the 'so and so'" e.g. "a man in an iron mask". With a definite description Russell means a single object on the form "the 'so-and-so' in the singular". This means that there can only be one instance of this object and that it has a specific property e.g. "the man with the iron mask". Something that fits into this description is known by description as opposed to known by acquaintance which is known to us by its sense-data or the memory or introspection of the sense-data. Also, the description is to be unique: there is only one man with an iron mask and it is the man with the iron mask. If there were more men with iron masks it would be an ambiguous description. We only know the man in the iron mask by his description and not by acquaintance. Seeing the man in the iron mask as a physical object I think that Russell wants to find a good way to describe objects that we don't have sense-data for. 

–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 dismisses that a true belief could be considered knowledge. I find it pretty straightforward that believing in something which happens to be true doesn't constitute knowledge. A belief may be deducted from past acquaintance and descriptive knowledge or reached without inference, intuitive knowledge. Any of these derivative beliefs will however still be just beliefs. The intuitively based derivatives are just as intuitive as their basis and in my opinion that doesn't count for much in a scientific context.

Russell furthermore talks about the nature of things being all the truth about that same thing. He states that with this assumption we can't know of that thing's nature at all unless we know all the thing's relation to everything else in the universe. If I were to interpret what Russell means by this I would say that it is irrelevant to pursue the nature of things. Truth is dependent on context. I do not believe that objects nor anything else possesses a truthful essence. I think that truths are ever-changing and that they may co-exist in contradiction to each other.