In this group of chapters, Carnap returns to the roughly the range of topics that he introduced in ch. 1. That chapter concerned laws and explanation while his focus here is causality; but the idea of a cause is closely related to explanation (think about the relation between “Why?” and “Because …”), and laws play an important role in Carnap’s account of causality.

Chapter 19 leads up to Carnap’s own definition of the relation between cause and effect (at the beginning of the first full paragraph on p. 194). When you reach that, think how his discussion in the earlier parts of the chapter served to motivate the various components of the definition.

In the time since this has been written, many people have come to see the examples of the different causes that might be cited for a given event as an indication that what counts as a cause or an explanation depends on the interest of the people to whom it is provided. One aspect of this is the idea that a cause or explanation is an answer to a why-question and that these why-questions typically take the form “Why … rather than …?” so what counts as a good answer depends on what the event to be explained is contrasted with. For example, a doctor might ask what caused a patient to die young of tuberculosis rather than having a normal life span or what caused a patient to die of tuberculosis rather than some other disease he or she was suffering from; and the answers to these questions are likely to be different. In light of what he says about the examples he considers on pp. 191f, think how Carnap might respond to these considerations and think also about what your own view is. That is, are ideas of cause and explanation relative someone’s interests or to what sort of why-question has been asked or do they concern absolute features of reality.

Chapters 20 and 21 both concern the idea of causal necessity. Carnap’s views about this might be puzzling since he seems to argue in ch. 20 that talk of causes implies no claim about necessity only to go on in ch. 21 to develop an idea of causal necessity. One way of harmonizing the two chapters is to see Carnap’s main point as his claim that “it is more fruitful to replace the entire discussion of the meaning of causality by an investigation of the various kinds of laws that occur in science” (p. 204). The sort of necessity he rejects in ch. 20 is one that would go beyond the content of laws (when these are expressed as a conditional generalizations), and the sort of necessity he embraces in ch. 21 is one that can be described in terms of a logical analysis of laws. You should ask yourself both whether you agree with Carnap’s critical arguments in ch. 20 and whether you agree with his constructive view in ch. 21. There are philosophers who would reject the whole idea of causal modality and others who would accept it but say that it leads to a concept that cannot be reduced to the logical form of laws.

Whether or not it provides the basis for a concept of causal necessity, the distinction between accidental universals and genuine laws is an important one. In his discussion of “nomic form” in the first part of ch. 21 Carnap suggests some grounds for making this distinction but suggests that there are other factors. Do you see any that you think should be added? (The idea of counterfactual conditionals that Carnap mentions on pp. 209-210 has received much attention since this book was written and is now often regarded as being at the heart of these issues.)

A related question, but one that might not be answered in quite the same way, concerns the generalizations that provide genuine explanations. It has been suggested that there is a sort of asymmetry here: a generalization that holds in two directions might provide an explanation only in one of them. A standard example is that, for a given position of the sun, we take the height of a flagpole to explain the length of its shadow but don’t take the length of the shadow to explain the height of the flagpole even though each can be deduced from other using laws.