Will Cliff
4/23/10
Logical Positivism
 Primarily empiricist point of view that knowledge comes from sensory
experience, yet uses mathematics as a tool as it is analytic a priori knowledge.
 First group to take a stance on Empiricism.
 Supported idea that the only source of knowledge is experience.
 Primary Doctines
o Analytic/Synthetic Distinction
o The Verification of Meaning
The Verification of Meaning
 A non-analytic statement is only meaningful if it is verifiable by a sense
experience.
 Example of a sentence that is meaningless according to its proponents:
o Freud’s Oedipus complex: it is a nothing-nothing statement because
the synthetic statement cannot be tested or proved.
o Not possible to test it, you can never really know what one really
thinks.
 Vague because:
o Practice v. principle
 Cant test whether or not there was a fly on Caesars nose.
 We cannot verify this NOW.
 The “able” means that in principle we are able to verity it. We
cannot put ourselves in a position where we could
observationally confirm a lot of synthetic statements.
o Phenomonalism: we try and verify things with our senses but our
senses could be wrong.
 We see a tree and that can be confirmed with our
senses, but how do we know that it isn’t a fake tree or
that we get a false sensory impression.
o The verificationist theory of meaning seems to be self-refuting in that
it is not easy to see how one could verify by sense experience that it is
the correct view of meaning.
 In-practice verifiability versus In-principle-Verifiability
o In practice verifiability states that currently we cannot verify a
statement that we may believe to be true…
o BUT then In principle verifiability comes into play because potentially
we could test this in the future with better technology.
 Example:
 The average atmospheric temperature on the nearest
extra-solar system planet is 150 degrees.
 As of now this isn’t verifiable because we cannot verify
this now, but maybe we could in the future.
Analytic versus Synthetic Statements
 Analytic Statement: a statement that is true or false just in virtue of their
meaning. Made to be true simply by the meanings of the terms it contains,
and as such it would plausibly be true no matter how the world might be
altered. When the world changes, its meaning remains the same… true or
false.
o Bachelor’s are unmarried.
o Triangles have 3 sides
 Synthetic Statement: a statement that is not analytic. It is not necessarily
true based on the meaning of the statement alone because its validity
changes when the world changes.
o The President of the United States is Barack Obama.
 There have been 50 presidents of the US—it is not
automatically Barack Obama.
A priori versus A posteriori
 A priori: a statement that is knowable independently of sense experience.
o You can determine that a 10 lb ball and a 5 lb ball will hit the ground
at the same time because if you cut the 10 lb ball in half the two pieces
they would hit the ground at the same time, so whether they are
attached into a 10 lb ball makes no difference.
 No need to test this with sense experience.
o Triangles have three sides.
o Triangles have 180 degrees.
 A posteriori: a statement that is knowable only via the senses.
How is the analytic/synthetic distinction relevant to the a priori/a posteriori
distinction?
 Generally its accepted that analytic is connected to a priori and synthetic is
connected to a posteriori.
 Analytic claims allow for non-mysterious a priori knowledge because they
can be accepted as false or true purely based on logic through the fact that it
is an analytic statement.
 The problem with a synthetic, a priori knowledge is that if a statement is not
meaningful (or you cannot determine whether or not it is true or false purely
based on the sentence) then it cannot be solved purely through logic without
sensory experience.
o Empiricists and logical positivists agree with this.
 The only reason for thinking there could be synthetic, a priori knowledge is
the viewpoint of Rationalists—people who believe that all knowledge can be
deduced by logic.
o Immanuel Kant, a rationalist, believed in synthetic, a priori
knowledge.
o His example used the statement, “Triangles have angles that sum to
180 degrees,” this isn’t analytic because most people only define a
triangle as a 3 sided polygon, not that its angles sum to 180 degrees.
Yet he can also prove it using a priori knowledge.
 The positivists say that a triangle isn’t technically 180 degrees based on
Einstein’s General Theory of Relativity that space is curved. This makes the
claim wrong that the sum of a triangle is always 180 degrees. This makes it
not a priori because its not perfectly true when you logically reason after
Einstein disproved it.
Quine’s Challenge to Logical Positivism
 The Quine-Duhem Thesis is an attempt to disprove the verificationist theory
of meaning and the analytic/synthetic distinction. It states that individual
synthetic statements alone do not carry enough information to be
individually testable. Need to be holistic—only test groups of sentences in
order to have empirical significance.
o The verificationist theory of meaning assumes the each synthetic
sentence has an empirical significance of its own… but Quine said that
we can only test groups of sentences.
 Example:
 There is a tree in front of me
 This doesn’t imply that I will see a tree in front of me
because it could be too dark to see it or I could have bad
eye sight.
 A large group of sentences as such would have more
empirical significance:
o There is a tree in front of me and it is not too
dark and my eyesight is good… etc.
 Quine’s beliefs threatened the analytic/synthetic distctions because claims
are groups of sentences, you cannot assume them all to be true and test them
individually so you can never know which is true. Quine believes that there
is nothing that is completely analytic.
Induction versus Deduction
 Deduction is if the premises are all true, then the conclusion has to be true as
well.
o This also means that if the premises are not true, then the conclusion
is not true.
o Examples:
 A=B, and B=C, then A=C
 T is true implies S is true as a conclusion, so if T is not true,
then S is not true as a conclusion.
 Socrates is a man, all men are mortal, so Socrates is mortal.
TRUE and deductive
 All birds can fly, penguins are birds, so Penguins can fly. FALSE
example of deduction because one premise is not true.
 Induction is an argument that isn’t deductive in the sense that the truth of the
premises does not guarantee the truth of the conclusion.
o This is because not all the premises have can be tested.
o Example:
 Newton’s Law of Universal Gravitation is about all bodies.
 But this makes it inductive because not all bodies have
been examined and tested. Despite being a very
accepted theory.
 All swans seen so far are white, so all swans are white.
 The problem with induction is that the conclusions that it draws aren’t
necessarily true.
 Types of Induction
o Enumerative Induction
 An induction that is a generalization.
 A group of various entities that have a certain combination of
similar properties and then a conclusion is made that claims
that everything has the same property as the first, second and
the whole first group.
 Example:
 Newton’s Law of Universal Gravitation because it
assumes all bodies have been tested.
o Abductive Inference
 Aka Explanatory inference
 We infer that the best explanation of a certain phenomenon is
true.
 Example:
 When there was evidence of layers of iridium in layers
of the earth’s crust that are 65 million years old,
scientists made the abductive inference that a meteor
hit earth 65 million years ago.
Hypothetico-Deductivism
 If one theory implies one thing, when another, different theory implying
another thing is confirmed as true, the in the slightest way the first theory is
slightly confirmed more true.
 Professor defines it as: “we confirm a generalization when one of its
consequences turns out to be true.”
 The problem is that even if you see an enumeration of various entities with
similar characteristics, it truly does not confirm in any way that all the
entities demonstrate the same characteristic.
 The problem with this is that it means that two completely different theories,
that are unrelated to say the least, can essentially slightly confirm each other
when one is confirmed true.
o Yet this confirmation really means nothing to strengthen any theory.
 Example of the problem:
o If a child only saw 1000 blue m&m’s, he would hypothesize that all
m&m’s are blue, but this theory is incorrect.
o Meaning that visually confirming that various entites have similar
characteristics still confirms nothing about the generalization.
Nelson Goodman’s “Grue” Problem
 An object is “Grue” if and only if it was first observed 2020 and is green, or if
it was not first observed before 2020 and is blue.
 While today the terms green and “grue” are logically equivalent
 Whether the statement holds true is partially determined by the language we
use.
o We tend to favor the “all emeralds are green” instead of “all emeralds
are grue.” Despite them both being completely equal and valid before
2020.
o This is because we believe that all emeralds will always be green after
2020, even though it is a inductive argument—meaning that there is
no way to prove that all emeralds wont turn blue after 2020—making
the “all emeralds are grue” make more sense.
 The solution to the problem is more complicated than just that favoring the
green is the answer. This is because today we think green makes more sense
because we believe there is no way that all emeralds are going to change to
blue in 2020. But since they are inductive statements and there is no way to
prove they are true, there is no way to prove that all emeralds won’t change
to blue in 2020, so potentially the all emeralds are green statement could
make less sense but we just don’t know it.
 We base so much today off of what we think we know when it is really an
inductive argument.
o Why do we think the world is so simple when we have no proof that it
really is?
The Demarcation Problem
 The problem trying to distinguish genuine science and pseudo-science.
 Popper believed that a theory is science if it is falsifiable, and that if it is not
falsifiable, then it isn’t science.
 Popper believed it needed to be falsified by observation, but the problem
theorizes that it could also be falsified by logic.
Karl Popper
 Popper was different than the Logical Positivists in that he wasn’t trying to
determine what sentences are meaningful—he was attempting to distinguish
science and pseudo-science.
o He believed there was no such thing as verification (or confirmation)
but instead falsification.
 He believed all induction was rational and unjustified.
o He believed it hasn’t been solved because it cannot be.
 “all emeralds are green” is not verifiable by induction even in
the weak sense that we have good, though not conclusive,
evidence for it.
 Believed in falsification not verification.
 Believed it was important in science because it doesn’t
require irrational induction but only requires
deduction.

Popper’s scientific method is that:
o A bold conjecture is made (a risky hypothesis)
o Next are the attempted refutations.
 Attempt to refute their own theories by experiments—trying
to falsify the hypothesis.
 When falsified, a new bold conjecture is made and if that isn’t
falsified it NOT accepted as true because that would be
induction. It has only not yet been refuted.
 One problem with this view is that if a hypothesis is falsified, according to
Quine it does not necessarily mean that the entire hypothesis is wrong
because there are multiple parts to a hypothesis.
o The conclusion still could be true and it could just be that one
presumption in the hypothesis is false. There is also no way to prove
which one is false.
o So it could be that one of the presumptions is false or that the
conclusion is false.
o Presented with this problem Popper said that the scientist would get
to choose… but why is that and how do you know what’s right?
 Another problem is that it is incredibly impracticale if you follow it strictly
because you can’t ever know anything is true from induction.
o Yet induction is a huge part of science so if this is true we would know
very little.
 Also, does unlikely mean falsification?
o You cannot just falsify a whole theory from one experiement… you
have to decide what to do—another problem as in “who are you to
decide?”
 According to Popper a scientists should not believe our best scientific
theories because he believes a scientists should come up with their own
scientific theories, make a bold conjecture and try and falsify them
themselves.
o This is incredibly impractical and no progress would be made.
Descriptive versus Prescriptive (or normative)
 Descriptive: what scientists do.
 Prescriptive (normative): what scientists should do (according to a point of
view, an opinion, in this case Popper.)
Pierre Duhem
 What is the method of physical discovery?
o First: reductio ad absurdum= hypothesis  contradiction. The
problem with this is the Holistic problem (too many things
surrounding the hypothesis to falsify just the hypothesis.)
o Second: list out all possible hypotheses, then eliminate by experiment.
But you cannot list out all the possible hypotheses… impossible.
o Third: build hypotheses from observations; symbolic translations?
Meaning there are many different ways to interpret the things you
observe.
o Concluded that we shouldn’t build theories based on observations, but
we should build a theory and then experiment it with observations
and experiements.
Questions:
1. Can you go over how Quines attack logical positivism threatens the
analytic/synthetic distinction?
2. Revie the problem with hypothetical deductivism?
3. What problem does the “Grue” problem generate for the justification of
induction?
4. ASK TA whether I should come up with our own examples or whether we can
use the ones given if we demonstrate understanding?