The most popular exposition of the Vienna Circle's Logical Positivism. My main purpose in these notes is to clarify for myself the differences between Ayer's understanding of logical positivism and my own notion of metaphysical positivism, with some remarks on my understanding of Carnap's position.
What is the purpose and method of Philosophy?
Rejection of the Metaphysical Thesis that philosophy affords us knowledge of a transcendent reality.
Kant also rejected metaphysics in this sense, but wheras he accused metaphysicians of ignoring the limits of human understanding, we accuse them of disobeying the rules which govern the significant use of language.
Adoption of verifiability as a criterion for testing the significance of putative statements of fact.
Distinction between conclusive and partial verification. No propositions can be conclusively verified.
For a statement of fact to be genuine some possible observations must be relevant to its truth or falsehood.
Examples of the kind of assertions familiar to philosophers which are ruled out by our criterion.
Metaphysical sentences defined as sentences which express neither tautologies nor empirical hypotheses.
Linguistic confusions the prime sources of metaphysics.
Philosophy provides not explicit definitions such as are found in a dictionary, but definitions in use.
Russell's "theory of descriptions" as an example of philosophical analysis.
Definition of an ambiguous symbol.
Definition of a logical construction.
Material things are logical constructions out of sense contents.
By defining material things in terms of sense contents we solve the so-called problem of perception.
A solution of this problem outlined as a further example of philosophical analysis.
Danger of saying that philosophy is concerned with meaning.
The propositions of philosophy are not empirical propositions about the way in which people actually use words. They are concerned with the logical consequences of linguistic conventions.
Rejection of the claim that `every language has a structure concerning which in the language nothing can be said`.
The words `true' and `false' function in the sentence simply as assertion and negation signs.
The criterion of validity of factual propositions is not purely formal.
No empirical propositions are certain, not even those which refer to immediate experience.
Observation confirms or discomfirms not just a single hypothesis but whole systems of hypotheses.
The `facts of experience' can never compell us to abandon a hypothesis.
Danger of mistaking synthetic for analytic propositions.
Hypotheses as rules which govern our expectation of future experience.
Definition of probability in terms of rationality.
Propositions referring to the past.
Sense contents as parts, rather than objects, of experience.
Sense contents neither mental nor physical.
Distinction between the mental and the physical applies only to logical constructions.
The existence of epistemological and causal connections between minds and material things open to no a priori objections.
Analysis of the self in terms of sense experiences.
A sense experience cannot belong to the sense-history of more than one self.
The substantive ego, a fictitious metaphysical entity.
Hume's definition of the self.
That the empirical self survives the dissolution of the body is a self-contradictory proposition.
Does our phenomenalism involve solipsism?
Our knowledge of other people.
How is mutual understanding possible?
Philosophy is not a search for first principles.
The function of philosophy is entirely critical. But this does not mean that it can give an a priori justification of scientific or common sense assumptions.
There is no problem of induction as ordinarily conceived.
Philosophising is an activity of analysis.
Most of those who are commonly thought of as great philsophers were philosophers in our sense, rather than metaphysicians.
Locke, Berkeley, Hume are analysts.
We adopt Berkeley's phenomenalism, without his theism.
And take a Humean view of causation.
Philosophy in our sense is wholly independent of metaphysics.
We are not committed to any doctrine of atomism.
The philosopher as an analyst is not concerned with the physical properties of things, but only in the way that we speak about them.
Linguistic propositions disguised in factual terminology.
As empiricists we must deny that any general proposition concerning a matter of fact can be known certainly to be valid.
How then are we to deal with the propositions of formal logic and of mathematics?
Rejection of Mill's view that these propositions are inductive generalisations.
They are necessarily true because they are analytic.
Kant's definitions of analytic and synthetic judgements.
Analytic propositions are tautological, they say nothing about any matter of fact.
But they give us new knowledge inasmuch as they bring to light implications of our linguistic usages.
Logic does not describe the laws of thought.
Not geometry the properties of physical space.
Our account of a priori truths undermines Kant's transcendental system.
How, if they are tautological, can there be in mathematics and logic the possibility of invention and discovery?
How does an empiricist deal with assertions of value?
Distinction between various types of ethical enquiry.
Utilitarian and subjectivist theories of ethics consistent with empiricism.
But unacceptable on other grounds.
Description between normative and descriptive ethical symbols.
Assertions of value are not scientific but `emotive'.
They are therefore neither true nor false.
They are partly expressions of feeling, partly commands.
Objection that this makes it impossible to dispute about questions of value.
Actually, we never do dispute about questions of value, but always about questions of fact.
Ethios as a branch of knowledge comprehended in the social sciences.
The same applies to aesthetics.
Impossibility of demonstrating the existence of a transcendent God.
Or even of proving it probable.
That a transcendental god exists is a metaphysical proposition, and therefore not literally significant. Saying this does not make us atheists or agnostics in the ordinary sense.
The belief that men have immortal souls is also metaphysical.
There is no logical ground for conflict between religion and science.
Our views supported by the statements of theists themselves.
Refutation from the argument from religious experience.
The nature of philosophy does not warrant the existence of conflicting philosophical "parties".
The conflict between rationalists and empiricists.
Our own logical empiricism to be distinguished from positivism.
We reject Hume's psychological as opposed to his logical doctrines.
To say that a thing exists is not to say that it is actually being perceived.
Things as permanent possibilities of sensation.
What is perceived is not necessarily mental.
Nor what is thought of exist.
Empirical grounds for supposing that things exist unperceived.
Monistic fallacy that all of a thing's properties are constitutive of its nature.
Illustrates the danger of expressing linguistic propositions in factual terminology.
Causality not a logical relation.
Empirical evidence against the monist's view that every event is causally connected with every other.
Philosophy as the logic of science.
Here we see presented as a central feature of logical empiricism the elimination of metaphysics. The verification principle is the tool deployed to effect that elimination. There seems to me to be here some ambiguity in the notion of transcendence. It is first described as going beyond science and common sense, and later as going beyond the phenomenal evidence. Since most people would regard science and common sense as routinely inferring to objects which are not entailed by the available phenomena, this is quite a big difference.
However, the verification principle is stated in a liberal form, which admits that for significance a proposition does not need to be conclusively verifiable or falsifiable, which Ayer says they never are. It is for this reason that Ayer says that his logical empiricism differs from positivism. So "going beyond" the phenomena in such a way as to fall foul of this weak verification principle may indeed involve going beyond science and common sense, and Ayer's empiricism is weaker in its proscription of metaphysics than some positivist philosophy.
This is a taster, and sets the tone. It give the impression that the central purpose is the negative one of detecting metaphysics, and that the tool to use for this purpose is the verification principle, as a criterion of significance.
This is not the flavour one gets from Carnap. Carnap, particularly the early Carnap, is reknown for sweeping dismissals of metaphysics, but if you read about what he says about purpose, and what he does towards realising the purpose, it is of an entirely different and much more positive character.
Metaphysical positivism is one step further still away from being primarily concerned with critique. In both these cases, though a critique motivates the work, the work itself is not seeking out and extirpating the bad, it is contributing to concepts, languages and methods which allow things to be done better.
Ayer distinguishes his logical empiricism from positivism on the ground that it does not require of an empirical proposition that it be conclusively verifiable, and therefore has a narrower conception of metaphysics (on its face, though perhaps not in practice). Metaphysical positivism would also by this criterion fail to be positivism since it does not even adopt the verification principle, and does admit metaphysics (of a kind). However, again, the practice may not be so distant.