Nelson Goodman - Induction and "grue"

Induction and "grue"

In his book Fact, Fiction, and Forecast, Goodman introduced the "new riddle of induction", so-called by analogy with Hume's classical problem of induction. He accepted Hume's observation that inductive reasoning (i.e. inferring from past experience about events in the future) was based solely on human habit and regularities to which our day-to-day existence has accustomed us. Goodman argued, however, that Hume overlooked the fact that some regularities establish habits (a given piece of copper conducting electricity increases the credibility of statements asserting that other pieces of copper conduct electricity) while some do not (the fact that a given man in a room is a third son does not increase the credibility of statements asserting that other men in this room are third sons). How then can we differentiate between regularities or hypotheses that construe law-like statements from those that are contingent or based upon accidental generality?

Hempel's confirmation theory argued that the solution is to differentiate between hypotheses, which apply to all things of a certain class, and evidence statements, which apply to only one thing. Goodman's famous counterargument was to introduce the color grue, which applies to all things examined before a certain time t just in case they are green, but also to other things just in case they are blue and not examined before time t. If we examine emeralds before time t and find that emerald a is green, emerald b is green, and so forth, each will confirm the hypothesis that all emeralds are green. However, emeralds a, b, c,..etc. also confirm the hypothesis that all emeralds are grue.

Goodman's example showed that the difficulty in determining what constitutes lawlike hypotheses is far greater than previously thought, and that once again we find ourselves facing the initial dilemma that "anything can confirm anything".

Despite this, Goodman said that we could limit claims to avoid creating a "class" or "type" of things.

We ignore these limits in day-to-day language. However, many disciplines (law, medicine, politics, and so on) restrict their hypotheses to what can be clearly proved.

People working in these areas treat their findings as contingent. They work successfully within the limits which the evidence seems to very firmly support. However, truth comes second to deciding the next step to take, after which the situation can be reassessed.