1. Sense data is the mental image we have in our minds about a real object. For example if I look at an apple, then I get a picture of the apple in my mind. That picture is green/red and round. This image in my mind is an example of sense data. These sense data are not the truth about the object it is the properties our mind has made up about the object.

Since two people don’t have the same experiences or the exact same sensation at the same time, Russell says that the sense data is personal.  The sense data can be alike though.

He introduces this notion to make us understand that things aren’t always as they seem to be. Our senses do not tell us the truth about objects but how we think the object is from previous experience.

2. A proposition is a description about an object; something is ”so and so”. This proposition may be true or false and can be a belief of something. A statement of fact is also a description about something but has to be able to be backed up by evidence or facts if anyone questions it. A proposition becomes a statement of fact when many prove it.

3. There are two kinds of descriptions; ambiguous and definite. An ambiguous description describes something on the form of  “a is so and so” and is only a description of something, while a definite description is on the form “a is the so and so” which is defining. “A man” is an ambiguous description and “the man with the iron mask” is a definite description.

A definite description is the description, we know that it is “the so and so” which means that there is only one object having this property.  The proposition “a is the so and so” means that a has the property so and so, and nothing else has.

4. A true belief is not a knowledge, we need proof to say that something is true.  When we read a text we make an interpretation of the text and form our own statement. We can know things that are translated from a statement in to our own opinions. In many cases we think we have learned a truth of a fact, when we actually have made our self a belief.

In an example Russell talks about a man who believes that the late Prime Ministers name began with a B, which was true since his name was Bannerman. But what if the man thought that Balfour was the late Prime Minister? Then his belief is still true, but would not be thought to constitute knowledge.