Thus to discuss conceptions of mass, of the atom, of affinity and so forth, as if one could derive from the scientific theories which elaborate them some information of immediate relevance for the philosopher, is to waste one's time; worse still, it is to become sterile and to discredit oneself. There is no more agreemetn or disagreement possible between the sciences and metaphysics than there is between two lines drawn on differetn planes. When once one has awakened, really awakened, to this truth, which is quite independent of the variety of philosophical opinions, it is impossible to understand how one could have believed the contrary. And then a great deal of time is saved which would have been simply wasted on false problemsna nd a great deal of misdirected effort.
[Maurice Blondel, "A Letter on the Requirements of Contemporary Thought and on Philosophical Method in the study of the Religious Problem," The Letter on Apologetics & History and Dogma, Alexander Dru and Illtyd Trethowan, eds. Eerdmans (Grand Rapids: 1994) pp. 131-132.]
Verily, verily, amen. I recall reading once in Etienne Gilson somewhere a discussion of the association of determinism with Newtonian physics. It is, in some sense, a real puzzle: there is nothing particularly deterministic about Newtonian physics; many who accepted Newtonian physics (I would go so far as to say the overwhelming majority) were not determinists, and were clearly not inconsistent in this; you can only get rationally from Newtonian physics to determinism by a vast number of controvertible suppositions; and so forth. So why did the association between Newtonian physics and deterministic metaphyics arise? Gilson points out that the source seems to have been a vague analogy. When determinists would appeal to Newtonian physics as proof of determinism, the inference from one to the other was not a rational one but an imaginative one, based on a strong felt analogy between certain aspects of Newtonian physics and certain aspects of their deterministic worldview. The inference consists entirely of this analogy; nobody did the hard rational work of building a rational inference. Newtonian physics suggested to the imaginations of determinists (and others, it should be said) certain things that felt or seemed similar to certain deterministic claims. The whole association was based on nothing stronger than a felt resemblance of structure between the scientific theory and the philosophical position; a felt resemblance which was taken for granted rather than rigorously and critically examined. Something very similar happened with quantum indeterminacy; some people, like Eddington, held that it refuted determinism and made room for free will. What was really going on was that, their imaginations having been trained by the previous analogy to associate certain aspects of Newtonian physics with determinism, when those aspects turned out not to show up in quantum mechanics, they made a similar sort of analogical leap in the opposite direction.
It has become more and more clear to me that this failing is extremely common. You can find it everywhere. Steady state theorists often opposed Big Bang cosmology simply because of a felt resemblance to a doctrine of creation; an analogical inference (and again, nothing more than an analogical inference) that seems to be very common. William Lane Craig holds that Big Bang cosmology contradicts the view that the universe has always existed; in fact, this is just analogical, as well, since the only rational way to get from Big Bang cosmology to the refutation of the claim that the universe has always existed is by way of a string of debatable suppositions. Some people think that evolutionary theory involves an attack on morals; what they really mean is that what they hear about evolutionary theory has a strong felt resemblance to an amoralistic worldview. Lindsay, in reply, says:
Simple Darwinism* tells me that every single human is literally family to me. Darwinism tells me that racism is crazy. Pace Genesis, Darwinism also reminds me that I'm not so different from a lot of other animals who are capable of feelings and therefore shouldn't be tortured, regardless of what any deities have to say about our respective statuses. I'm not saying that Darwinism is the only road to those conclusions, just that these Darwinian-inspired tenets are at least as good prima facie reasons for tolerance as anything in Genesis.
[The footnote at the * just points out that the label 'Darwinism' is being borrowed from the context of the discussion, rather than having any deep meaning for Lindsay's argument.]
But evolutionary, of course, says nothing whatsoever about these things. What Lindsay means is that certain aspects of evolutionary theory have a strong imaginative resemblance to a moral view of the human race in which all human beings would morally be able to be counted as family, animals are not so morally different from human beings. These are, as Lindsay rightly says, "Darwinian-inspired"; they are not Darwinian. The tenets are only based on what is felt by the imagination to be a strong resemblance between the physical structure and process indicated by evolutionary theory and the moral structure and process of certain moral views. People in the early twentieth-century who read evolutionary theory in exactly the opposite way, as licensing racism and human superiority over animals, were making an argument of exactly the same sort. The move from evolutionary theory to a moral claim would rationally involve many complicated and difficult-to-defend suppositions; imaginatively it just takes a sense of similarity.
Nor is ethics the only area in which this is true. One of Darwin's most brilliant philosophical insights about how evolutionary theory could be established was in his recognition of the need sharply to distinguish imagination and reason in one's approach to the theory of natural selection. Natural selection, properly speaking, is unimaginable: there are simply too many factors involved in it for anyone to imagine anything remotely close to accurate. People who try to understand natural selection by imagining it will get it wrong. But reason can go where imagination cannot; it can find ways to get around and overcome the complexity of the topic. The path of reason is much, much harder than that of imagination, requiring much, much more careful argument. But Darwin rightly recognized that it is on reason, not imagination, that the theory of natural selection had to be built. If you try to convey the theory by imagination, you will fail and you will mislead people, because you will only convey a caricature that is vaguely analogous to the theory of natural selection, not the theory itself.
I am far from saying that these analogical leaps are always wrong, or even that they are always bad. Hume is right, I think, that the problem with analogical inference is not that it is weak (some analogical inferences are very strong) but that, on its own, it is very uncertain: we cannot say from the inference itself whether it is strong or weak. Only when you begin actually tracing the rational path the analogical inference leaps over can you begin to tell whether the analogy is actually relevant. I do think that these imaginative moves are almost ineliminable; they are an artefact of the way the human mind works, and, recognized for what they are, they can sometimes serve a heuristic function, or (used carefully) they can sometimes be a useful way to shorten an otherwise extremely complicated discussion that can (for the moment) be glossed over. But they need to be recognized for what they are: leaps based on a subjective sense of resemblance, not on any real rational analysis.