Short Answer Questions (submit online)
- What is the difference between a formal and a causal/empirical idealisation?
- Explain how John Norton distinguishes between approximations and idealisations.
- How can idealisations lead one to make incorrect inferences?
For Further Discussion
- They're everywhere? In lecture we saw several examples of idealisations: Newton's law of inertia, economic models that presume the rationality of human agents, the use of the real number field in physical descriptions of objects like spheres, and so on.
- How ubiquitous are these kinds of idealisations? Can you think of any description in which an idealisation is not applied?
- Suppose that, as an idealisation, someone were to make some quick but effective calculations using the Ptolemaic (geocentric) astronomical system. Is this idealisation (or some aspect of it) "illigitimate" as a means for describing the world?
- What (if anything) do you think generally characterises an illigitimate idealisation?
- Formal vs Empirical Idealisations. Suppose you have a formal description of a system and an empirical test of that description. For example, your formal description might be Galileo's law of fall, and your empirical test might be the Brian Cox experiment in NASA's evacuated test chamber.
- Is it possible to have the formal idealisation without an empirical one?
- Is it possible to have the empirical idealisation without the formal one?
- Is there any relationship between the concept of a formal idealisation and that of an empirical one, or are they totally independent? Is one more problematic than the other, or is their philosophical status similar?
- Approximation vs Idealisation. Norton suggests that we distinguish approximations from idealisations in terms of a "target system" that we wish to describe.
- Norton's definition hinges on whether or not our description "refers" to a target system. What does he mean by that?
- How can we tell whether or not a theoretical description is referring to our target system or not? Is there a way to recognise this among the theoretical terms? Do you have to ask the person doing the describing? Norton does not clearly specify the answer to this question — can you?
- Norton says that the "infinitely large sphere" is a dangerous idealisation in a way that an infinitely long cylinder is not. Explain.
- In the article, Norton discusses the difference between an infinitely long ellipsoid and an infinitely long cylinder, and finds that the two objects differ in their description of the ratio of the surface area to the volume. Is this a problem for the idealisation? Why or why not?
- The laws of physics lying. Do concerns about idealisations suggest that we should be antirealists about the fundamental laws of science? Or do they make it easier for us to be realists? What (if anything) is the relationship between idealisations, approximations and scientific realism?