In yesterday's session of the Logos Seminar, Roman Frigg made the interesting suggestion that scientific models -such as ball-and-stick molecular models or simple pendula, with their massless strings and their point masses- should be understood as being similar in kind to literary fictions -such as Sherlock Holmes or Godzilla. Furthermore, he proposed that the best treatment for these is one along the lines of Walton's acts of make-believe.
I had doubts about one of the arguments he presented for treating models as fictions:
(The Semantic Argument) The simple pendulum equations are not true of anything -they would only apply to pendula with a massless string and a point mass, shielded from all forces but a uniform gravitational field, or something like that. Therefore, between the equations and real pendula we must postulate an imaginary something -a scientific model- to which the equations would faithfully applied, if it existed.
In fact, Roman's aim for the talk was to consider the relation between ourselves and the scientific model -relation he spelled out in terms of acts of make-believe- and not the relation between model and world.
But I would have said there is another option to deal with the lack of conformity between the simple pendulum equation and real pendula: the relevant singular terms in the equations do really refer to pendula; it is just that the equations misrepresent them. Actually, they don't misrepresent them that much; this is why the equations are useful. Wouldn't this get rid of models-as-fictions in the case of pendula?
A way to drive this point home, maybe, is to consider a history book in which several things are said about World War II, some of which are false: that Spain sent troops to Germany, maybe. Couldn't we mount an analogue to the Semantic Argument above to the effect that there is a fictional war involved in our understanding of the text?
(The Semantic Argument - WWII version) The sentences in the history book are not true of anything -they would only apply to a war in which Spain did send troops to Germany. Therefore, between the book and the real war we must postulate an imaginary something -a fictional war- to which the sentences would faithfully applied, if it existed.
But we feel no temptation to postulate such a fictional war: it is just that the book misrepresents WWII.
Another question in this connection: does it follow, if Roman is right, that there is a fictional model between ball-and-stick molecular mock-ups and real molecules, one in which atoms are spherical and rigidly bonded to one another? I'm not sure that it follows, but if it does, that is surely less natural than simply say that such a ball-and-stick mock-up truly represents the molecule of, say, cyclohexane, just like a map of the London Tube truly represents the London Tube.