empirical—derived from experience.

a posteriori—Latin from ‘what comes after.’ An a posteriori proposition is one that can be known to be true,
    or false, only by reference to how, as a matter of contingent fact, things have been, are, or will be.

--have been, “Alabama was in the Confederacy.”
--is, “Cal Poly is a university.”
--will be, “Cal Poly will have new parking structure within five years.”

rational—derived from reason.

a priori—Latin from ‘what comes before.’ An a priori proposition is one that can be known to be true, or
false without reference to experience, except in so far as experience is necessary in understanding.

     2+2=4
     Bodies are extended in space.
     A triangle has three connected sides.

a posteriori and a priori—a distinction between kinds of knowledge and how one may acquire its truth.
    You have knowledge that is based upon experience and knowledge that is not. You have truth that
    is contingent upon experience and truth that is not.

analytic—a  sentence where the concept of the predicate is contained in the subject.

  “All bachelors are unmarried males.”
     This sentence will always be true in virtue of definition and meaning alone. Bachelor=unmarried male

  “All triangles have three connected sides.”
     This sentence will always be true in virtue of definition and meaning alone. triangle=three sided connected
        thing

tautology—Frege defined all mathematical truths as those that are both analytic and tautological.
    Tautologies are generally defined as statements true on all value assignments under main logical operator.

    2 = 2, 2 + 2 = 4, If Scott is teaching then Scott is teaching.  All rectangles have four connected sides.

 The truth-conditions for the conditional --> are:
  p   q           p --> q
  T   T          T   T  T
  T   F          T   F  F
  F   T          F   T  T
  F   F          F  T  F

Logically, through the use of truth-tables, where the main logical operator is a conditional, a simple tautology
 is:
p          p --> p
T          T  T  T
F          F  T  F

A more complex tautology, consider the following:
(p & q) --> p

We have added a new logical operator called the conjunction and it is best represented by the term ‘and.’
We first need to know the truth-conditions of the ‘&.’

p  q     p & q
T  T      T T T
T  F      T F F
F  T      F F T
F  F      F F F

And we previously saw the truth conditions for the conditional.

  p   q           p --> q
  T   T          T   T   T
  T   F          T   F   F
  F   T          F  T   T
  F   F          F  T   F

Now we have the truth-conditions for our two logical operators. We begin by with anything inside the
 parentheses and work outwards. Thus, the main logical operator in this case is the conditional and
 that’s where we will need to look for all T’s.

p q   (p & q) --> p
T T    T T T   T  T
T F    T F F   T  T
F T    F F T   T  F
F F    F F F   T  F

truth-conditions: statements are either true or false depending upon their conditions which make them
    true or false. For Ayer there are two types of truth conditions:

empirical—under what conditions of the world is statement ‘x’ true (or potentially true) and under which
    conditions is it false.

     “Scott is in class.”
       This can be known by direct observation or by appeal to evidence.

mathematical statements—mathematical statements are tautologies, thus they are always true.

synthetic—a sentence where the concept of the predicate is not contained in the subject.

     “All students have good grades.”
      This sentence can be false or true depending up the the applications of it and the way the world is.

     “Rocks are heavy.”
       This sentence can be false or true depending upon the rocks are being referenced.

metaphysics—Ayer is seeking to redefine ‘metaphysics’ in terms of significant statements in language—
    empirically verifiable (in principle) statements and tautologies.

principle of verification—a sentence’s meaning is determined by its method of verification. If you don’t
    know how to verify a statement, there is a good chance it does not have any meaning.

Ayer states, “We need only to formulate the criterion which enables us to test whether a sentence
    expresses a genuine proposition about a matter of fact, and then point out that the sentences under
    construction fail to satisfy it.”(35)

 For example, from Hegel’s Philosophy of Right, p. 45

“Since matter in itself does not belong to itself.”

 What does this statement mean? How would you go about verifying or try to find the truth-conditions, i.e.,
    what makes this statement true or false?

Another example, from Hegel’s Philosophy of Right, p. 30

 “It is the will whose potentialities have become fully explicit which is truly infinite, because its object is itself,
    and so is not in its eyes an ‘other’ or a barrier; on the contrary, in its object this will has simply turned its
    back on itself.”

 So, the thinking philosopher trying to give a shot at understanding this passage will require making sense
    of the word ‘will’. Hegel defines the ‘will’ as: “The will contains the element of pure indeterminacy or that
    pure reflection of the ego into itself which involves the dissipation of every restriction and every content
    either immediately presented by nature, by needs, desires, and impulses, or given and determined by
    any means whatever.  This is the unrestricted infinity of absolute abstraction or universality, the pure
    thought of oneself.”

 My question is then, how would we even attempt to verify or ascertain the truth conditions of this statement?
 Specifically, how would we attempt to verify that the will contains the element of pure indeterminacy and
    that this is the same thing as the pure reflection of the ego into itself involving dissipation?

 Ayer would claim statements like these are grammatically correct yet they have no meaning. The
    appearance of the statement as meaningful is misleading because although it satisfies our rules of grammar,
    it is not verifiable, thus it has no meaning—and we should discard it.

He states, (1) “The criterion we use to test the genuineness of apparent statements of fact is the criterion of
    verifiability. We say that a sentence is factually significant to any given person, if and only if, he knows how
    to verify the proposition which it purports to express—that is, if he knows what observations would lead him,
    under certain conditions, to accept the proposition as being true, or reject it as being false. (2) If, on the
    other hand, the putative proposition is of such a character that the assumption of its truth, or falsehood, is
    consistent  with any assumption whatsoever concerning the nature of his human experience, then, as far as
    he is concerned, it is, if not a tautology, a mere-pseudo proposition. The sentence expressing it may be
    emotionally significant to him; but it is not literally significant. (3) We enquire in every case what observations
    would lead us to answer the question, one way or the other; and, if none can be discovered, we must conclude
    that the sentence under consideration does not, as far as we are concerned, express a genuine question,
    however strongly its grammatical appearance does.” (35)

There are three parts to this criterion.

(1) A statement is a fact if and only if someone knows under what conditions the statement is true or false.

(2) Notice the qualifier here of ‘future experience.’ Ayer’s point is that we have no assurance of future events
    being like past ones, and that we can’t use past experiences to justify the same type of experiential
    regularity in the future.

 For example, you assert, “I feel I will graduate next year.” For Ayer this is not an empirically verifiable
    proposition, thus it is a  pseudo-proposition. However, more importantly, notice he says, ..it may be emotionally
    significant to him; but it is not literally significant.” Statements like these assert your feelings about the
    future, however your feelings are not empirically verifiable, thus statements with expressions like these are
    not factually significant.  Ayer’s emotive theory of ethics is the result of his view of language, and (2).

(3) The role of procedure.  What observation or set of observations would lead us to answer the question that
    the statement is factually significant. If none (obs.) can be found, then the statement may look significant,
    but it is not.

Two-types of Verifiability: Practical and In Principle.

Practical—statements which can be verified with enough work.
 “Kilaminjaro is 12,345 feet.”
 “San Diego is 651,522 feet from Riverside.”
 “Cal Poly is a school in California.”
 “Atoms exist.”
 “Judy Miles is Chair of the Philosophy Department.”
 “Cellular phones cause brain cancer.”

In Principle—statements that are factually significant, but where, for any number of reasons, practical
    observations cannot be made.

 “There is a big lake on the planet Mars.”

 To verify this statement, we have to know what a ‘lake’ is, what ‘Mars’ is and what would count as a ‘lake
    on Mars.’ We can in principle do this if we had the means to get to Mars.

 “There is a big lake on planet Twin Earth.”

To verify this statement, we have to know what a ‘lake’ is, what ‘Twin Earth’ is and what would count as
    a ‘lake on Twin Earth.’ We cannot in principle do this because ‘Twin Earth is not an empirical object
    such that it is available for in principle verification. The grammar misleads us in this case, where as
    it didn’t in the former.

Other statements that are in principle verifiable.

“The temperature of the Earth’s core.”
We know that to measure the temperature, we would need some type of measuring device and a way to
    get it there.

“Evolution adequately accounts for the fossil record.”
We know what would count as representative examples of the correct chain of evidence in the fossil record.

Two further qualifications of ‘verifiable.’ Ayer distinguishes two senses of the word, strong and weak.
  strong—a statement is strongly verifiable, if and only if, its truth can be conclusively established in
        experience.
   weak—a statement is weakly verifiable, if and only if, its possible for experience to render it probable.

Ayer rejects strong verifiability because it leads to the very kind of statements that he is seeking to reject.

Consider the statement,

 “All women are mortal.”

To use the criterion of strong verifiability, we would have to examine every single woman in history, however
we know this is impossible. What Ayer points out is that statements like these assume a law like characteristic,
allowing one to make claims about the future based upon the past. However, we already know that statements
about the future, are at best, expressions of emotions or attitudes, and not expressions of fact. So strong
verifiability ends up undermining itself.

Weak verifiability simply asks, “Would any observations be relevant to the determination of its truth or falsehood?”
If the answer to this question is ‘no’, then we can conclude that the statement is nonsensical.(38)

Ayer’s goal is make philosophy a genuine branch of knowledge distinct from metaphysics—or at least the
kind of metaphysics he finds objectionable. “Metaphysics” for Ayer is a pejorative term, it is bad for something
to be metaphysical.

Ayer defines a metaphysical sentence as one that, “purports to express a genuine proposition, but does, in
fact, express neither a tautology nor an empirical hypothesis. And as tautologies and empirical hypotheses
form the entire class of significant propositions, we are justified in concluding that all metaphysical assertions
are non-sensical.

Ayer goes on to give examples of metaphysical statements in the history of philosophy.

Substance/Essence—That which makes something an ‘x’ versus a ‘y’.

Humans have an essence that they share. This use of ‘essence’ indicates that we all have ‘x’ and without ‘x’
    we would fail to be humans.

 Ayer’s objection: Humans have sensible properties, e.g., skin color, eye color, height, sex, etc… As a
    feature of our language, we use words to indicate these properties, however, they also indicate a thing-itself
    (an essence). The thing-itself must be recognized as a false reference, and it leads one into metaphysical
    illusion—there are essences.  The word 'human' refers to a set of properties that are observable. Ayer will
    refer to these properties that are observable in experience as ‘sense data.’

So we might conclude with the following, Ayer states, “As to the validity of the verification principle, in the form
which we have stated it, a demonstration will be given in the course of this book. For it will be shown that all
propositions, which have factual content, are empirical hypotheses; and that the function of a rule is to provide
a rule for the anticipation of experience. And this means that every empirical hypothesis must be relevant to some
actual, or possible experience, so that a statement which is not relevant to any experience is not an empirical
hypothesis, and accordingly has no factual content. But this is precisely what the principle of verifiability asserts.” (41)

Summary: Ayer is attacking traditional metaphysics where language goes beyond its simplistic function.
He believes there are two classes of significant statements: empirically verifiable ones, and tautologies.
If a sentence is not one of these two classes, it is a metaphysical sentence and should be cast aside.
He supports both practical verifiability and in principle verifiability. Finally, his chosen version of a criterion of
verifiability is weak verifiability because it doesn’t suffer the problems of strong or conclusive verifiability.
 

Ayer has a distinctive view on what philosophy is supposed to be.

What it is not.

a) A search for first principles and a deductive system. He directs this at Descartes who believed
you could derive all human knowledge from his cogito—I think therefore I am.

“The belief that it is the business of the philosopher to search first principles is bound up with the
familiar conception of philosophy as the study of reality as a whole. And this conception is one which
it is difficult to criticize because it is so vague. If it is taken to imply, as it sometimes is, that the
philosopher somehow projects himself outside the world, and takes a bird’s eye view of it, then it
is plainly a metaphysical conception. And it is also metaphysical to assert, as some do, that ‘reality
as a whole’ is somehow generically different from the reality which is investigated piecemeal by
the special sciences.” (47)

Ayer makes two points here: 1) the impersonal perspective leads one to metaphysical problems.
Think of the free will/determinism debate and how the conceptions of free will and causal determinism
appear to conflict. 2) To assume that a complete conception of reality is different than understanding
particular parts of it, is to buy into the wrong metaphysical picture.
How can a phrase like “…reality as a whole” be verified?

What it is.

1. It is a critical activity consisting of:

a) Ascertaining whether someone’s beliefs are consistent.
    [Are all of your beliefs true?]
b) Ascertaining what the relevance of the criteria which are used in determining the truth or falsehood
   of any given proposition.[What counts as acceptable evidence in determining whether something is true or false?]
c) Showing that experience can justify beliefs.
    [If our experience can't justify our beliefs, what can?]
d) Accepting common sense beliefs except where the  grammatical structure of the statement misleads.
    [Humans may share a similar physical appearance, but that does not mean they share an essence.]
e) Analysis and clarification of words and concepts.
    [How do we use our words and concepts?]

On (b) and (c) Ayer states: “We may look to the philosopher to show us what we accept as constituting
sufficient evidence for the truth of any given empirical proposition. But whether the
evidence is forthcoming or not is in every case a purely empirical question.” (48-49)

So, a philosopher on Ayer’s account is someone who does a-e.

Question: How does Ayer's account of what it is to be a philosopher differ from Epictetus'?

The Problem of Induction

Induction in general is defined as a general law is inferred from a particular instance(s).

Problem of Induction—the problem of finding a way to prove that certain empirical generalizations that are
derived from past experience will hold in the same way in the future. (49)

For example. In the past we know that a dropped object will hit the ground. However, do we know
for certain that this will occur in the future?

Problem of Induction in Argument Form (from Sober)

P1—All observed rocks that have been dropped have hit the ground.
P2—All dropped rocks have been observed.
----
C—All dropped rocks, past, present, or future, will fall to the ground.

The problem is P2. This premise is false, rocks in the future have not been observed, nor have all in
the present or past, been observed.  P2 assumes something called the Principle of the Uniformity of
Nature, or that the future will always be like the past. Thus, the conclusion is false and we have no
absolute certainty that a dropped rock will fall to the ground.

Another way of stating the Problem of Induction. To make a claim about the future based upon the
past, you must use induction. However, you cannot justify this use of induction without using induction
to prove it. It is paradoxical. It is this paradoxical nature that Ayer notices and he labels the problem
of induction a “fictitious problem” since it is incapable of being solved.

The Problem of Induction was first formulated by David Hume. Here is the argument in detail.

Hume's Skeptical Thesis About Induction (all from Sober pp.184-187),

There are two arguments.

Generalization Argument
G1-I have observed numerous emeralds, and each has been green.
-----
-----
GC-Hence, all emeralds are green.

Prediction Argument
P1-I have observed numerous emeralds, and each has been green.
-----
-----
Hence, the next emerald I see will be green.

In both of these arguments, we believe that the conclusion is rationally justified, given the premise.
Hume will go against this and argue that we are not rationally justified in accepting that the premises
support the conclusions. Hume's general view is that there is no rational justification for the beliefs
we have about predictions or generalizations.

So, in the Generalization Argument, Hume is saying something like the following. From individual
instances of observation of something, we cannot make a generalized claim about those things.
And, in the Prediction Argument, Hume is saying something like the following. From individual
instances of observation of something, I cannot predict that the next thing will have the property
or properties of those instances.

Why not? Why can't you correctly infer those conclusions?

Hume thinks that both assume an implied premise, something called the Principle of the Uniformity
of Nature. This principle (PUN) states that we must assume that the future will be like the past,
or our future experiences will be like our past experiences based upon some principle or law that
guarantees this uniformity.

Try this on the Prediction Argument.

Prediction Argument
P1-I have observed numerous emeralds, and each has been green.
P2(PUN)--Every emerald I have observed in the past is green and every emerald I will see in the
future  will be green.
-----
-----
Hence, the next emerald I see will be green.

Hume's contention against the Prediction argument is simple. Without PUN, the past would be no
guide to the future. Hume's Skeptical Argument can now be formulated in detail.

S1--Every inductive argument requires PUN as a premise.
S2--If the conclusion of an inductive argument is rationally justified by the premises, then those
premises must themselves be rationally justifiable.
S3--So, if the conclusion of an inductive argument is justified, there must be a rational justification
for PUN.
S4--If PUN is rationally justifiable, then there must be a good inductive argument or a good
deductive argument for PUN.
S5--There is no good inductive argument for PUN, since any inductive argument for PUN will be
circular.
S6--There cannot be any good deductive argument for PUN, since PUN is not a priori true, nor does
PUN deductively follow from the observations we have made to date.
S7--So, PUN is not rationally justifiable.
----------
Hence, there is no rational justification for the beliefs we have that take the form of predictions
or generalizations.

Going back to the notion of no absolute certainty, Ayer recognizes this as an outcome of not accepting
strong induction, so he formulates something currently known as ‘fallibilism.”

He states, “We are entitled to have faith in our procedure just so long as it does the work which it is
designed to do—that is, enables us to predict future experience, and so to control our environment.
Of course, the fact that a certain form of procedure has always been successful in practice affords no
logical guarantee that it will continue to be so. But then it is a mistake to demand a guarantee where it
is logically impossible to obtain one.” (50)

No guarantees, but our procedures work and are fallible.

Ayer’s Phenomenalism

Phenomenalism—an analysis of physical object propositions.

“…we know that is must be possible to define material things in terms of sense contents,
because it is only by the occurrence of certain sense contents that the existence of any material
thing can ever be in the least degree verified.”

Sense-content—provided by experience through sight, sound, smell or any of the other
sensory modalities.

“For the philosopher, as an analyst, is not directly concerned with the physical properties of things.
He is concerned only with the way in which we speak about them.”

“Thus, to ask what is the nature of a material object is to ask for a definition of ‘material object,’ and
this, as we shall shortly see, is to ask about how propositions about material objects are to be translated
into propositions about sense contents.

Explicit Definitions—synonyms, Cardiologist = heart-doctor

Definitions in Use—“We define a symbol in use, not by saying that it is synonymous with some other
symbol, but by showing how the sentences in which it significantly occurs can be translated into equivalent
sentences, which contain neither the definiendum itself, nor any of its synonyms.

Definiendum—word being defined
Definiens—definition

Ayer’s point is that an in-use definition will not contain any reference to the original term. It works
something like this:

*She has a table in her room.

Our purpose is to translate the material object ‘table’ into sense contents.

We could substitute the following for ‘table’: round, dark blue, 3 legged and speckled thing.

**She has a round, dark blue, 3 legged speckled thing in her room.

Ayer wants to say that ‘table’ in * is a logical construction of the sense contents of **.  So, ‘table’ is a
definition in use/logical construction of the appropriate sense contents.

Notice the link here Ayer has established. He has related our objective experience directly to language
through sense- content and definitions in use. Remembering back to the principle of verification, meaningful
language is empirically related language. When language is not related to experience, either in practice or
in principle, language no longer has the link for meaning. Thus, his claim, that metaphysical sentences, or
those that go beyond experience are non-sensical—they don’t have the link.