"The business of the natural philosopher is to construct theories which will 'save appearances'. Most of us first meet this expression in Paradise Lost (viii, 82) and most of us perhaps originally misunderstood it. Milton is translating (Greek script), first used, so far as we know, by Simplicius in his commentary on the Aristotlean De Caelo. A scientific theory must 'save' or 'reserve' the appearances, the phenomena, it deal with, in the sense of getting them all in, doing justice to them. Thus, for example, your phenomena are luminous points in the night sky which exhibit such and such movements in relation to one another and in relation to an observer at a particular point, or various chosen points, on the surface of the Earth. Your astronomical theory will be a supposal such that, if it were true, the apparent motions from the point or points of observation would be those you have actually observed. The theory will then have 'got in' or 'saved' the appearances.(*AO Barfield, Saving the Appearances)
But if we demanded no more than that from a theory, science would be impossible, for a lively inventive faculty could devise a good many different supposals which would equally save the phenomena. We havce therefore had to supplement the canon of saving the phenomena by another canon -- first, perhaps, formulated with full clarity by Occam. According to this second canon we must accept (provisionally) not any theory which saves the phenomena but that theory which does so with the fewest possible assumptions. Thus the two theories that (a) the bad bits in Shakespeare were all put in by adapters, and (b) that Shakespeare wrote them when he was not at his best, will equally 'save' the appearances. But we already know that there was such a person as Shakespeare and that writers are not always at their best. If scholarship hopes ever to achieve the steady progress of the sciences, we must therefore (provisionally) accept the second theory. ....
In every age it will be apparent to accurate thinkers that scientific theories, being arrived at in the way I have described, are never statements of fact. That stars appear to move in such and such ways, or that substances behaved thus and thus in the laboratory -- these are statements of fact. The astronomical or chemical theory can never be more than provisional. It will have to be abandoned if a more ingenious person thinks of a supposal which would 'save' the observed phenomena with still fewer assumptions, or if we discover new phenomena which it cannot save at all.
This would, I believe, be recognized by all thoughtful scientists today. It was recognized by Newton if, as I am told, he wrote not 'the attraction varies inversely as the square of the distance', but 'all happens as if' it so varied.
It was certainly recognized in the Middle Ages. 'In astronomy," says Aquinas,' an account is given of eccentrics and epicycles on the ground that if their assumption is made (haec positione facta) they could also be saved by some different assumption'. The real reason why Copernicus raised no ripple and Galileo raised a storm, may well be that whereas the one offered a new supposal about celestial motions, the other insisted on treating this supposal as fact. If so, the real revolution consisted not in a new theory of the heavens but in 'a new theory of the nature of theory.'*
More on the Copernican Revolution, and Saving the Appearances, here:
But in reality Copernicus's book marked a sea change in human thought, one that caught the universities even more off guard than the Church. Owen Barfield, in his fascinating book Saving the Appearances, calls it “the real turning-point” in the history of science: “It took place when Copernicus (probably—it cannot be regarded as certain) began to think, and others, like Kepler and Galileo, began to affirm that the heliocentric hypothesis not only saved the appearances, but was physically true...It was not simply a new theory of the nature of celestial movements that was feared, but a new theory of the nature of theory; namely, that, if a hypothesis saves all the appearances, it is identical with truth.”
Copernicus had delayed the publication of his book for years because he feared, not the censure of the Church, but the mockery of academics. It was the hide-bound Aristotelians in the schools who offered the fiercest resistance to the new science.
The Boy Scientist, which I was going to have Kieron read next year, has a similar perspective on the Galileo affair. It regards the change as a good thing, however, while Lewis seems to have mixed feelings.
One more idea in this line, from Lewis' epilogue -- I wish I could quote the whole thing, but I shall have to clip out excerpts that don't represent his entire process of thought:
"The nineteenth century still held the belief that by inferences from our sense-experience (improved by instruments) we could 'know' the ultimate physical reality more or less as, by maps, pictures, and travel-books, a man can 'know a country he has not visited; and that in both cases the 'truth' would be a sort of mental replica of the thing itself. Philosophers might have disquieting comments to make on this conception; but scientists and plain men did not much attend to them."
(he goes on to summarize some of the ways that this idea of the past century is not quite accurate, and then goes on)
He goes on to discuss how the main change in the "Model" wasn't the phenomena so much as how the phenomena was regarded. For an example, Darwin's theory of evolution was not, in itself, new. It was the empirical data he collected and described vividly and intelligently, and the way his presentation bore out the new Model of the rationalist age, that accounted for at least some of the influence he has had on our age.
"Without a parable modern physics speaks not to the multitudes. Even among themselves, when they attempt to verbalise their findings, the scientists begin to speak of this as making 'models'. It is from them that I have borrowed the word. But these 'models' are not, like model ships, small-scale replicas of the reality. Sometimes they illustrate this or that aspect of it by an analogy. Sometimes, they do not illustrate but merely suggest, like the sayings of the mystics. An expression such as 'the curvature of space' is strictly comparable to the old definiton of God as 'a circle whose centre is everywhere and whose circumference is nowhere.' Both succeed in suggesting; each does so by offering what is, on the level of our ordinary thinking, nonsense. By accepting the 'curvature of space' we are not 'knowing' or enjoying 'truth' in the fashion that was once thought to be possible.
It would therefore be subtly misleading to say 'The medievals thought the universe to be like that, but we know it to be like this'. Part of what we now know is that we cannot, in the old sense, 'know what the universe is like' and that no model we can build will be, in that old sense, 'like' it.
Lewis says that the Great Minds of each age tend not to be affected as exclusively by the "Model" of the age.
"The great masters do not take any Model quite so seriously as the rest of us. They know that it is, after all, only a model, possibly replaceable."(p 14).
And later (p 222):
I am only suggesting considerations that may induce us to regard all Models in the right way, respecting each and idolising none. We are all, very properly, familiar with the idea that in every age the human mind is deeply influenced by the accepted Model of the universe. But there is a two-way traffic; the Model is also influenced by the prevailing temper of mind.
This is a theme he also express in the famous Introduction to "On the Incarnation", which is famous because it so nicely expresses what is the goal of liberal education -- a mind which engages with truth, but does not jump too early to conclusions based on its own natural and temporal bias:
Every age has its own outlook. It is specially good at seeing certain truths and specially liable to make certain mistakes. We all, therefore, need the books that will correct the characteristic mistakes of our own period. And that means the old books. All contemporary writers share to some extent the contemporary outlook - even those, like myself, who seem most opposed to it. Nothing strikes me more when I read the controversies of past ages than the fact that both sides were usually assuming without question a good deal which we should now absolutely deny. They thought that they were as completely opposed as two sides could be, but in fact they were all the time secretly united - united with each other and against earlier and later ages - by a great mass of common assumptions. We may be sure that the characteristic blindness of the twentieth century - the blindness about which posterity will ask, "But how could they have thought that?" - lies where we have never suspected it, and concerns something about which there is untroubled agreement between Hitler and President Roosevelt or between Mr. H. G. Wells and Karl Barth. None of us can fully escape this blindness, but we shall certainly increase it, and weaken our guard against it, if we read only modern books. Where they are true they will give us truths which we half knew already. Where they are false they will aggravate the error with which we are already dangerously ill. The only palliative is to keep the clean sea breeze of the centuries blowing through our minds, and this can be done only by reading old books. Not, of course, that there is any magic about the past. People were no cleverer then than they are now; they made as many mistakes as we. But not the same mistakes. They will not flatter us in the errors we are already committing; and their own errors, being now open and palpable, will not endanger us. Two heads are better than one, not because either is infallible, but because they are unlikely to go wrong in the same direction.