Quine, “Natural Kinds” Some Problems of Induction: (1) The New Riddle of Induction (Goodman) Goodman proposes a new predicate: grue. X is grue if and only if it is examined before t and is green, or it has not been examined before t and is blue. Now, let’s suppose t is now. The following inductive inferences would seem to be equally well justified. Emerald 1 is green, emerald 2 is green, … So, the next emerald will be green. Emerald 1 is grue, emerald 2 is grue, … So, the next emerald will be grue (i.e. blue).

In other words, we are equally justified in expecting the next emerald to be grue as we are in expecting it to be green. But, if it is grue, it is blue and not green. Goodman’s questions are then the following: What makes a statement genuinely lawlike? What allows us to recognize some predicates (like green) as good, respectable predicates and to disregard other predicates? What makes one predicate projectible, another not?

Goodman: “The real inadequacy of Hume’s account lay not in his descriptive approach but in the imprecision of his description. Regularities in experience, according to him, give rise to habits of expectation; and thus it is predictions conforming to past regularities that are normal or valid. But Hume overlooks the fact that some regularities do and some do not establish such habits; that predictions based on some regularities are valid while predictions based on other regularities do not… To say that valid predictions are those based on past regularities, without being able to say which regularities, is thus quite pointless. Regularities are where you find them, and you can find them anywhere.” (4th ed., p. 82)

Back to Quine “What makes Goodman’s example a puzzle, however, is the dubious scientific standing of a general notion of similarity. [¶] The dubiousness of this notion is itself a remarkable fact. For surely there is nothing more basic to thought and language than our sense of similarity; our sorting of thing into kinds.” (234a) There is something wrong with taking similarity to be a matter of set membership. Similarity is a matter of degrees; set membership isn’t.

Similarity is, however, necessary for the learning of language. For one learns a language (wholly or in part) through ostension. A standard of similarity is in some sense innate. (236a)

“To trust induction as a way of access to the truths of nature … is to suppose, more nearly, that our quality space matches that of the cosmos. The brute irrationality of our senses of similarity, its irrelevance to anything in logic and mathematics, offers little reason to expect that this sense is somehow in tune with the world – a world which, unlike language, we never made. Why induction should be trusted, apart from special cases such as the ostensive learning of words, is the perennial philosophical question of induction.” (237ab)

Philosophy and science work together and are in the same boat… Neurath’s boat. “For me, then, the problem of induction is a problem about the world: a problem of how we, as we now are…, in a world we never made, should stand better than random or coin-tossing chances of coming out right when we predict by inductions which are based on our innate, scientifically unjustified similarity standard. Darwin’s natural selection is a plausible partial explanation.” (237b)

“Things are similar in the later or theoretical sense to the degree that they are interchangeable parts of the cosmic machine revealed by science.” (240a) “In general we can take it as a very special mark of the maturity of a branch of science that it no longer needs an irreducible notion of the similarity and kind. It is the final stage where the animal vestige is wholly absorbed into the theory. In this career of the similarity notion, starting in its innate phase, developing over the years in the light of accumulated experience, passing then from the intuitive phase into theoretical similarity, and finally disappearing altogether, we have a paradigm of the evolution of unreason into science.” (241b) Oh, really??