Positivism vs Realism
James Francis Lyons-Weiler
weiler at ERS.UNR.EDU
Sun Dec 14 15:12:45 CST 1997
On Sun, 14 Dec 1997, Tom DiBenedetto wrote:
> > If you are saying that hypotheses of convergence that
> > are retained as result of a parsimony analysis are not
> > corroborated as hypotheses of convergence by the parsimony "test",
> huh? We do not begin with any hypotheses of convergence. They are a
> result we are forced to accept when we encounter incongruence.
I never quite understand how a scientific inference leads
one to be forced to accept anything, if it's Popperian...
> > then you must also be saying that hypotheses of homology that
> > are retained are also not corroborated.
> huh? Since your premise is wrong, the conclusion is meaningless.
There is not a whit of difference in the empirical content
of the two following statements:
states A and B are homologous
states A and B are not convergent
They simply refer to different processes rendering their
distribution. If, as you claim, cladistic parsimony is
Popperian, then the logical framework affords the corroboration,
not the scientist. Therefore, either converges are just as
corroborated as hypotheses of homology (after the p "test")
or neither are corroborated. We can't decide willy-nilly
whhen which evidence (test statements) is relevant to
which hypotheses. That's just not science.
> There are no convergences to be corroborated before the test is run.
They either exist, or they do not.
> > Popper and Miller's proofs in the early '80s show clearly
> > that when a test only serves to restate the obvious, (1)
> > no corroboration results,
> and you think that a specific phylogenetic hypothesis is ever
Sure- taxon a is the sister taxon to B, to exclusion of
all other taxa...
> > (2) the test was not a critical test,
> given the number that are falsified, how can you claim the test isnt
Apparently falsified! And again, you are offering an
inductive justification - hardly Popperian.
> > (3) time is better spent either thinking of new and
> > bold hypotheses or devising more critical tests that
> > surpass the no longer salient ones in their revelations.
> so let me hear your bold hypothesis for the data of character
OK- Ho. There will be no significance difference between
the degree of implied nestedness in data set A and that
which may be expected by chance alone...
> > We need only use tests that are set up to tell
> > us if and when a significant level of congruence exists.
> > Parsimony doesn't address this.
> But that is another issue Your significance test is not going to
> yield a set of relationships. That is what we are after in
> systematics, y'know....
Not just any set of proposed relationships - the
most accurate possible seems the goal...
> >> When something is labeled homoplasy and we are forced to accept
> >> an ad hoc explanation for its presence in the data, we are
> >> acknowledging that it has failed to be corroborated by out test - it
> >> is a falsification. How can this be seen as dismissing Popperian
> >> corroboration?????
> > Because if it to be dismissed as a hypothesis of homology,
> > it must be a hypothesis of convergence.
> ???? If data cannot be explained by the tested hypothesis, then we
> need a new (smaller scale) explanation to account for it. This is not
> in any way non-Popperian.
I disagree - it is completely ad-hoc.
> "a high probability is a dubious reward for saying very
> little, or nothing. In other words, the rule 'Obtain high
> probabilities' puts a premium on ad hoc hypotheses. All this presents
> a most uninspiring picture of science- a picture, moreover, that does
> not in the least resemble the original. Indeed, what makes the
> original so inspiring is its boldness; its boldly conceived
> hypotheses, boldly submitted to every kind of criticism - to every
> refutaton we can think of, including the most severe tests....."
> "Since testability in its turn can be measured by the content
> of the theory, and since content, in its turn, can be measured by the
> absolute logical improbability of the theory, content and
> improbability stand in the same close relation to degree of
> corroboration as does testability itself."
The first quote does not equate boldness with testability-
it is more compatible with the following
" If hypothesis h is bold, the degree of corroboration
is higher than if it had had a high logical probability.
Of course, this would require that h be testable..."
Your use of the second quote is of interest, because
it reveals you confusion between "corroboration" and
"corroborability". The statement, reworded with
proper predicates, is
Testability is linked to the content and improbility
(boldness) of a hypothesis. Since the content
of a hypothesis determines its testability, and
the content (amount of information we stand to
aqauire if the hypothesis survives the test)
determines the boldness of the hypothesis, content
and boldness are as important to the determination
of the degree of corroboration of the hypothesis
should it in fact survive the test.
Boldness and degree of falsification achieved may be
linked, and bold hypotheses may be easier to test -
but falsification itself does not demand boldness.
> "..in order that [the hypothesis] should be maximally
> corroborable, its content or degree of testability must be maximal"
> "...corroborability equals testability and empirical
> "Why [do] scientists invaribly prefer a highly testable
> theory whose content goes far beyond all observed evidence to an ad
> hoc hypothesis, designed to explain just this evidence, and little
> beyond it, even though the latter must be more probable than the
> former on any given evidence"
> Boldness clearly relates to hypotheses which are improbable on the
> background knowledge alone; they are the opposite of ad hoc
> hypotheses which say very little.
No - you're wrong here. Ad-hoc hypotheses may be bold;
in fact all hypotheses (ad-hoc or not) have some inherent
degree of boldness. It's a lost cause to claim that
ad-hoc hypotheses and bold hypotheses are antitheses.
> degree of corroboration, C(h,e,b)= p(e,hb)-p(e,b) should enable you
> to see this. (The denominator is merely a normalizing factor)
> This can be related to parsimony as follows:
> "It can be shown that what is usually called the simplicity
> of a theory is associated with its logical improbability.....This
> indeed, allows us top deduce,....why it is always advantageous to try
> the simplest theories first. They are those which offer us the best
> chance to submit them to severe tests; the simpler theory has always
> a higher degree of testability than the more complicated one."
that only means they are easier to test - not that they
are magically better corroborated than more complex
tests that have also survived a critical test.
> Cladistics entails a bold conjecture, a simple theory, maximally
> testable (all of our homology hypotheses are valid statements of
> evolutionary relationships).
This has already been falsified.
>. Parsimony is the implementation of the
> test of congruence; a test directly deducable from the notions of
> "organism" and descent.
Tests that provide a greater empirical content
given the same data now exist - and they are also
based on the premise that characters are inherited
through time but place no limit on the degree of
modification and allow for its misleading effects.
why use parsimony as a test when it has such narrow scope?.
Alternative explanations for parts of the
> data are taken up as necessary in light of the results of the test. I
> dont see how this research program can be ignored unless you are
> willing to deny the notion of descent as a factor which can order
> homologies in a hierarchial manner.
I am willing to not deny it - but I am not willing to deny
much else that could have occured, either - the more
complex possible pasts that envelope and include
simple hierarchical sorting of characters. In not
allowing for the corroboration of hypotheses of convergence,
the parsimony "test" lacks imagination.
> > Some bold hypotheses can be ad-hoc,
> No. Ad hoc hypotheses are inherintly unbold. They account for
> specific phenomena and say nothing beyond that. Boldness refers to
> the scope of explanation that a hypothesis attempts.
OK - let's stop restating our position and get down
to contrived examples.
My hypothesis is whether or not pigs fly. So, I go about,
and I'm real good about, and check out plenty of pigs -
and I see none that fly. I may even go so far as to
examine the repetoire of every pig on the planet. If I
want an ad-hoc hypothesis, I only need to say that
pigs fly under circumstances that prevent us from
detecting them. this is a low-content, untestable
ad-hoc hypothesis that saves my hypothesis (to no one's
satisfaction, I hope).
Now for an example of an ad-hoc hypothesis that is
not bold. I examine the distribution of a species,
and look to environmental factors. Say it's a tropical
species. I'm about finished with my Ecological Monographs
ms and new records of the species turn up in the Arctic,
but that the populations are now extinct..
All of my data suggest that the species' limits are
defined by a narrow regime of climate and vegetation. And
yet there are the records. I can't perform any common
garden experiments - so I claim waif dispersal as my
hypothesis. It's not particularly outlandish; in fact,
it's the most reasonable hypothesis I can think of.
If I hypothesized that aliens manipulated the species'
occurences, now that's a bold ad-hoc hypothesis.
> huh? I have consistently said the opposite.
> Bold hypotheses are bold because they have high information
The information content of a hypothesis is one term
you seem to consistenly misuse. It is the amount of
new knowledge that would be aquired if the test is passed -
i.e., the information content is the potential consequences
of the hypothesis.
. Ad hocs have low information content.
This is correct - but only because they are not falsfifiable.
(it's an abuse of the logic, but correct).
> > It is clear that the only useful
> > bold hypotheses are the testable ones, but that's
> > only because they are hypotheses, and this is true of
> > any hypothesis...
> No, boldness and testability are inherintly linked.
No, boldness and degree of corroboration are linked
> re, cladograms
> > It is far better and more accurate to say that they are
> > hypotheses - to be tested in the future by independent
> > means - than to say that they are phylogenies, which
> > is downright misleading.
> Misleading to who? They are phylogenetic hypotheses. OK?
Misleading to the uninitiated, who look at the dialogs on
methods and conclud for themselves that if a tree is
published, then the phylogeny is known. BAD for funding,
and quite inaccurate.
> > the "test" you rely on
> > will pass any data matrix with variable states -
> > with or without a remarkable degree of congruence
> > (remarkable in the Popperian sense).
> it will report the degree of corroboration of the hypotheses. You are
> intent on making a judgement as to whether that degree is
> significant. That is a different question. Whether it is or isnt
> significant by your criterea, the results are not to be ignored in
> favor of a less corroborated hypothesis.
Your conclusion is a non-sequitur; so even when there is
no remarkable congruence, you're going to talk about it
anyway? (Remarkable in the Popperian sense). In face of
the results of a test that have dismissed the hypothesis
of siganificant congruence, you're going to press on
and summarize what amounts to noise?
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