When I was reading Greats at Oxford, there was a philosophy don called H W B Joseph who used to instruct his pupils on philosophical problems. Among these it was always said that he would catechise them on the rational nature of our belief in the sequence in natural science which we call cause and effect, that is the belief that identical 'causes' (I put the word for this in purpose in inverted commas)produce identical effects. The pupils would invariably reply with some reference to Newton, the falling apple, and the 'law' of gravity ('law' also in inverted commas), meaning of course the invariability with which objects fall downwards rather than upwards. 'But surely' Joseph would reply to this ingenuous approach 'it should have caused him increasing surprise'.
There is, I believe, no answer to this argument unless, of course, we have what, in discussing the nature of human understanding, Locke called an 'innate idea', at least in the field of the observable, that things make some sort of sense, and that at least to some limited extent our reason can achieve it. In the field which is open to observation, measurement, and repeated experimentation we can readily accept this. It is indeed the hypothesis upon which the whole dramatic development of the physical sciences is based.
(The first paragraph in this quotation appears to be corrupt in the online version; the phrase "produce identical effects" seems to have been dropped down a line, thus leaving a sentence fragment and creating an incoherent jumble. I have moved it to where it appears to belong.) Of this Gracchi says,
Now this is a reversion to a kind of theory of ideas- a Platonic sense that a word describes exactly the idea behind it and that idea is reflected in the world. It is interesting that Hailsham comes to argue this because the position he advocates is easily refuted and as problematic as any naive support for induction.
Such an argument for instance neglects the facts that we do not use these words to always embody the same ideas.
I don't think this gets Hailsham quite right, though. What Hailsham is advocating is not Platonism but rationalism, and while rationalists can be Platonists, they need not be. The argument is that science and experiment (and later morality and other things) is not a mere matter of habituation; it requires positing that the world is rational enough that we can understand it by reason. In other words, you can't just discover the nature of the world by being a passive empirical observer; you have to suppose, as a sort of act of recognition, that the world is intelligible. Thus Hailsham suggests that the 'innate idea' we have is "that things make some sort of sense, and that at least to some limited extent our reason can achieve it." This is a fairly mild conclusion, and well short of Platonism. (And, I would suggest, given that Hailsham doesn't need a full-blown Platonism to make the basic parity argument he is trying to make, namely, that it makes sense to hold that there are objective moral truths for the same reason that it makes sense to hold that there are objective physical truths, Platonism would be overkill.) Thus, while the argument is fairly limited (parity arguments usually are), I don't think Hailsham supposes, as Gracchi suggests, the notion that words about the world are stable; rather, his argument requires that words about the world make sense, which is a slightly different thing.