
Grue and Bleen: New riddle of induction - shry4ns
https://en.wikipedia.org/wiki/New_riddle_of_induction
======
aggerdom
I found the SEP article to be a much better explanation of the issues posed
[1]. Wish Goodman was known more widely for his other work though. Had some
fascinating work trying to establish mereology as an alternative to set
theory. And he takes an interesting approach elsewhere by grounding
epistemology within aesthetics to some degree. Essentially making true and
false subsets of "rightness" and "wrongness". One example iirc we could call a
painting "jazzy" and it applying more or less right about it's subject but not
necessarily capital T true. Would recommend the Partially Examined Life
episode on his epistemology.

[1]
[https://plato.stanford.edu/entries/goodman/#NewRidInd](https://plato.stanford.edu/entries/goodman/#NewRidInd)
[2]
[https://partiallyexaminedlife.com/2010/10/31/episode-28-nels...](https://partiallyexaminedlife.com/2010/10/31/episode-28-nelson-
goodman-on-art-as-epistemology/)

~~~
whatshisface
Attempts at building in smoothness to logic never seem very useful to me,
because true/false based logic already supports real numbers and probabilities
as well as you could hope it to. If anything the real discovery of symbolic
logic was that you don't need smooth primitives to build arguments about
smooth things - it was obvious from the beginning that you could assign
something that was one of two things to one of two symbols, but the
realization that you could also do math and physics that way came much later.

------
Strilanc
The apparent paradox is that the choice of blue/green vs grue/bleen appears
symmetric: green="grue if before 2028 else bleen" whereas grue="green before
2028 else blue". But then why do we strongly prefer to make predictions using
green/blue instead of grue/bleen?

One way to resolve this paradox is to translate the terms into the raw
language of physics, at which point it's obvious which one is simpler. More
concretely, imagine trying to make a camera that recognizes "bleen" vs making
a camera that recognizes "blue". Which camera only works if you include a
clock? More abstractly, I would say that the Solomonoff complexity (aka
algorithmic complexity) of bleen is higher than blue (for basically any
programming language or hardware you will run into). Therefore you prefer
blue/green.

Yes, one can generalize the paradox by reformulating all of physics or all of
computer architecture to be based on the before/after 2028 distinction. And
yet, it does seem that that would make the physics harder and the hardware
more expensive, right? There seems to be an objective sense in which nature is
built around blue/green rather than grue/bleen.

------
mannykannot
I do not follow the objection to this response (at the top of the section
"Responses"):

 _" x is grue" is not solely a predicate of x, but of x and a time t — we can
know that an object is green without knowing the time t, but we cannot know
that it is grue. If this is the case, we should not expect "x is grue" to
remain true when the time changes. However, one might ask why "x is green" is
not considered a predicate of a particular time t - the more common definition
of green does not require any mention of a time t, but the definition grue
does._

Surely "x is green" is not considered a predicate of a particular time t
simply because it isn't, by definition, and the fact that grue and bleen are
defined as such is simply being used in a faulty analogy that is beside the
point?

It continues _this response also begs the question because blue can be defined
in terms of grue and bleen, which explicitly refer to time_ \- but blue, so
defined, loses any dependence on time even if it is nominally a parameter, and
so can be used in inductive arguments with respect to time in ways that would
be invalid for grue and bleen.

~~~
BlackFly
I agree, I think grue and bleen were constructed so that green and blue could
be redefined in terms of these new time dependent predicates to confuse the
fact that the original colors are not time dependent. In math it is completely
normal to write down some complicated formula of time dependent functions and
get a result which is independent of time, otherwise there could never be
energy conservation for example.

There are conventional time dependent predicates like a person's name that
nobody has a problem intuiting that induction fails for (many people take
their spouse's name after marriage or return to their original name after
divorce). It seems like these predicates were invented just to try to confuse
what it means for a predicate to be time dependent.

------
whatshisface
>* Clearly, the predicates grue and bleen are not the kinds of predicates we
use in everyday life or in science,*

I would argue that this situation actually does show up in every-day life and
science. Any situation where your coordinate system changes from one arbitrary
thing to another will result in a situation where the name, place or other
quality you assign to something "changes" without any real change being
involved. I think that a lot of philosophical problems can be reduced to the
verbal equivalent of switching between arbitrary coordinate systems.

------
nathias
Induction is a heuristic, it establishes a pattern but not it's necessity.

------
lisper
Induction [1] is logically invalid, full stop. It was thoroughly debunked by
Karl Popper, whose theory was popularized by David Deutsch in his book, "The
Fabric of Reality". The easiest way to see that induction is invalid is to
observe that the sun has risen in the east every day for the last few billion
years, but it is not valid to conclude that the sun will continue to rise in
the east forever. (It won't.)

The grue/bleen riddle was also debunked by Deutsch with the pithy slogan,
"Languages are theories." The words you use to describe your theory are not
arbitrary. The concepts they stand for can themselves be judged in the same
terms that the theory overall is judged by, namely, do they have explanatory
power? "Green" and "blue" have explanatory power. They sum up complex physical
processes in a very compact form. "Grue" and "bleen" do not. There are in fact
blue and green things in the world, and physics can explain _why_ there are
blue and green things. But there are no grue or bleen things, and Goodman
cannot justify why he wants to insert an arbitrary time parameter into his
terminology. The grue/bleen theory can be rejected _on those grounds alone_.

There are some legitimately time-dependent terms in use, for example,
"President of the United States", or "main-sequence star". But the time-
dependence of both of those can be justified in terms of phenomena that
actually occur in the world.

\---

[1] Note that in the context of Goodman, this means _logical_ induction
([https://en.wikipedia.org/wiki/Inductive_reasoning](https://en.wikipedia.org/wiki/Inductive_reasoning)),
not _mathematical_ induction
([https://en.wikipedia.org/wiki/Mathematical_induction](https://en.wikipedia.org/wiki/Mathematical_induction)).
The former is invalid, the latter is not.

~~~
sonusario
_... but it is not valid to conclude that the sun will continue to rise in the
east forever. (It won 't.)_

Can you use induction in a valid way to invalidate induction?

~~~
lisper
No. Induction is invalid, full stop. It cannot be validly used to demonstrate
_anything_.

~~~
mrec
The point sonusario is making is that your assertion about the future
behaviour of the Sun is based on our understanding of physics, and physics is
itself inherently inductive - it's an abstraction and formalisation of
empirical experience. If we'd consistently made very different observations of
the world, we'd have come up with different physics, which would make
different predictions.

In my view saying things like "induction is invalid" is a bit of dead end,
rather like Cartesian doubt. It's not that it's _wrong_ , more that you can't
go anywhere interesting from there, unless you abandon your own principles and
start wibbling about God and the natural light and pineal glands.

~~~
lisper
> physics is itself inherently inductive

No, it isn't. It is _explanatory_. You need to read Deutsch and/or Popper. The
argument is too long to reproduce in an HN comment.

------
_nalply
grue is difficult to translate to German because a naive substitution would
yield grau (grün/blau), but grau is grey. How would you translate grue to
German?

~~~
theoh
Blün?

~~~
thaumasiotes
...then how would you translate bleen?

~~~
theoh
Apparently you just avoid naming the other term (if my rudimentary scanning of
this German webpage is correct):
[https://www.sapereaudepls.de/2018/01/20/goodman-
paradoxon/](https://www.sapereaudepls.de/2018/01/20/goodman-paradoxon/)

Blün is even in the Wiktionary:
[https://en.wiktionary.org/wiki/blün](https://en.wiktionary.org/wiki/blün)

