be derived from experience (see Hume's fork). One does not experience the causal connection between a hammer impact and the formation of a bruise. All that is observed are distinct events, occurring at the same place and time (Constant conjunction). Because one observes events of this type, one is led by induction to suppose that like causes will result in like effects, and from this one infers the notion of causation. This does not mean Hume doubted that one material object was able to cause a change or movement in another material object. It means that insofar as one talks about some cause resulting in some effect, it is not something one has learned of the world that is talked about because it is not derived from experience. Rather, one is talking about a feature of one's thinking which one is inclined to discuss as if it were a feature of the world. In short, when one believes one has observed a causal connection all one really has experienced is a conjunction between two separate events. One can only know about the world through experience, so causation as a feature of the world is something unknowable to a human being. The projectivist theory of probability What does it mean to say that the probability that a coin lands heads is ½? One might think that the coin will either land upward or it will not, the probability is not a feature of the world, but rather just a measure of one's own ignorance. Frank Ramsey (see his collected papers, edited by D. H. Mellor) and Bruno de Finetti, developed projectivist theories of probability in the early twentieth century. To explain their theories, the concept of degree of belief must first be introduced. Consider for example that a person has a degree of belief of 1 in a particular proposition if they are completely convinced of its truth. For example, most people have a degree of belief of 1 in the proposition that 2+2=4. On the other hand, a person has a degree of belief 0 in a proposition if they are utterly convinced of its falsity; most people have a degree of belief of zero in the proposition that 2+2=5. Intermediate values are possible. A man who thinks that his dog has stolen the sausages, but is not completely sure, might have a degree of belief of 0.8 in the