Logical Positivism – Summary

(This summary was produced for my introductory classes)

Logical Positivism, A. J. Ayer – Summary

©Peter Sjöstedt-H


–       Logical Positivism, also known as Logical Empiricism, is a philosophy developed in the early 20th Century, notably by Moritz Schlick. It was also, amongst others, influenced by the work of Bertrand Russell (1872 – 1970) and Ludwig Wittgenstein (1889 – 1951).

–       One of the most important Logical Positivists was A. J. Ayer who, in 1936, released his groundbreaking book, ‘Language, Truth and Logic’.

–       The other leading Logical Positivist, Moritz Schlick (1882-1936) was called to Vienna University in 1922. Other logical positivists gathered around him here, something which led to ‘the Vienna Circle’: a group associated with logical positivism.

–       The philosophy that is Logical Positivism has many far-reaching implications regarding ethics, aesthetics and theology.

–       The main tenet of logical positivism is that language causes many illusions. When we properly analyze a proposition, we find that some are literally nonsense.

  • They can be neither true nor false, and are thus grammatical trickery.
  • This too applies to questions: some are meaningless (e.g. “Does God exist?”)


Language, Truth and Logic (1936)


–       Ayer begins his book by accusing metaphysicians of making sentences which have no meaning.

–       He says that for a sentence to be literally significant, meaningful, it must conform to certain criteria.

  • Ayer goes on to formulate this criteria, he calls it the criterion of verifiability:

–       ‘We say that a sentence is factually significant [meaningful] … 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.’ (p.16)

  • i.e. a sentence only has meaning if it can be proved true or false by observation.

–       Thus, a question is genuine only if it can be observed true or false.

–       It is important to note that a sentence’s observation should at least be possible in principle. This gives it genuiness: verifiable in principle.

  • Ayer’s example is the proposition ‘that there are mountains on the farther side of the moon.’ (p.17)
  • Although (at the time) that proposition was not observed/verified, it was still verifiable in principle: it was a possibility that the farther side of the moon could be observed.
    • Therefore the proposition was meaningful: it was in principle able to give a truth or falsity, even though it had not done so at the time. It was verifiable in principle, if not in practice.

–       An example of a proposition that is meaningless would be, say, “God works in mysterious ways.”

  • This proposition is not verifiable even in principle.
  • What observations could prove it either true or false? None. It is therefore a meaningless proposition.


–       Further qualifying his verification principle, Ayer distinguishes between strong and weak verifiability.

  • ‘A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established in experience. But it is verifiable, in the weak sense, if it is possible for experience to render it probable.’ (p. 18)

–       Schlick adopted the strong sense.

–       Ayer adopts the weaker sense for the following reasons:

Universal Propositions (“all”)

  • Scientific laws, i.e. propositions such as ‘arsenic is poisonous’, ‘all men are mortal’, ‘a body tends to expand when heated’, all are true only by induction.
    • We could never observe every incident of arsenic intake; it cannot be verified conclusively to be true but only probable.
  • Some logical positivists have therefore said that such proposition are, in fact, nonsense (albeit an important type of nonsense!)
  • But Ayer, adopting weak verification, does not consider them nonsense because they are in principle possible to observe to be true or false to a high probability.

Historical Propositions

  • Another reason Ayer adopts the weaker sense is because of propositions about the past.
  • How could one verify that England was conquered in 1066 by the Normans, through observation?!
  • Ayer states that through historical records, archeological finds, geological studies, historical events can be at least rendered highly probable (but never certain).
    • Propositions about the past are thus verifiable through records, etc., and although this is weak verifiability, it is not nonsense.

–         ‘Accordingly, we fall back on the weaker sense of verification. We say that the question that must be asked about any putative statement of fact is not, Would any observation make its truth or falsehood logically certain? But simply, Would any observations be relevant to the determination of its truth or falsehood? And it is only if a negative answer is given to this second question that we conclude that the statement under consideration is nonsensical.’ (p. 20)

–       Ayer calls verifiable propositions experiential propositions.

–       There is another type of proposition that is also meaningful, however, but not experiential, and that is a tautology.

  • A tautology is where the predicate is already in the subject. It is thus an analysis of the subject and therefore also known as an analytic proposition.
    • E.g. “All bachelors are unmarried”, “A square has four sides.”
    • I.e. true by definition.

–       ‘Tautologies and empirical hypotheses form the entire class of significant propositions’ (p. 24)


–       Ayer’s next task, he says, is to show why nonsensical propositions come to be made.

–       He says that language creates illusions which give people metaphysical beliefs.

  • He gives the example of the metaphysical term, ‘substance’.
  • In our language we cannot speak about the properties of ‘something’ without introducing a word which appears to stand for thing itself (as opposed to anything that may be said about it).
  • I.e. when I speak about something, I can give all ‘its’ properties: (It is blue, hot, round, soft, etc.), but because our language must use the word ‘its’, one is led to believe that if one takes away all properties of that something, a kind of pure substance remains. The ‘thing-in’itself’.
  • ‘It is true that in talking of “its” appearances we appear to distinguish the thing from the appearances, but that is simply an accident of linguistic usage … the metaphysician fails to see this because he is misled by a superficial grammatical feature of his language.’ (p. 25)

–       So a proposition such as “Things-in-themselves have a noumenal existence” is nonsensical (as it is not verifiable in principle, nor tautological) and this is understandable because the metaphysician has been duped by grammar.

  • Nietzsche expounded this grammatical delusion 30 years before (1880s).

–       Another example is that of ‘being’ or ‘existence’

  • There have been many philosophical conjectures about the nature of existence.
  • Existential propositions have the same grammatical structure as attributive propositions:
    • “Martyrs exist” (e p) & “Martyrs suffer” (a p)
  • But, as Kant showed, existence is not an attribute. Existence is a covert assertion in an attributive proposition (it must exist to have an attribute).
  • If existence were an attribute it would mean that all existential propositions were tautologies (whose truth were not touched upon: anything could be asserted as existent: “spaghetti monsters exist”), and all negative existential properties would be self-contradictory (“The spaghetti monster doesn’t exist” = contradiction if existence is an attribute of the subject.) This is not the case: the last proposition is not self-contradictory.

–       [This grammatical point also does way with the famous ‘ontological argument’ for the necessary existence of God as propounded by St Anselm & Descartes.]

–       ‘The postulation of real non-existent entities results from the superstition … that to every word or phrase that can be the grammatical subject of a sentence, there must somewhere be a real entity corresponding. For as there is no place in the empirical world for many of these “entities”, a special non-empirical world is invoked to house them.’ (p.27)

–       This can apply to both theological propositions and ethical propositions.

Chapter 6: Critique of Ethics and Theology


–       A. J. Ayer’s Logical Positivism endorses a meta-ethic called Emotivism (developed later by C.L. Stevenson).

–       His is a critique against normative ethics, prescriptive ethics. As such his account of ethics is also know as descriptive. It is a non-cognitive ethic.

  • I.e. his criticism of ethics leads to emotivism.

–       Ayer begins by saying that there is a common supposition that our knowledge is of two kinds:

  • Questions of empirical fact
  • Questions of value

–       Questions of value are questions about the value of actions (ethical value) and the value of art, beauty (things of aesthetic value).

–       But this latter set of questions surely undermines the whole philosophy of logical positivism because a value proposition cannot be verified in principle (or by definition/analytically).

–       Therefore, Ayer says he must give an account of propositions of value.

–       He begins this account by generalizing that ethical (& aesthetic) propositions are not literally meaningful but are simply expressions of emotion which can be neither true nor false.

–       As such, ethical philosophy only compromises meta-ethics – normative & practical  ethics is an illusion.

–       But the question now to be answered is: why are moral propositions not experiential propositions, propositions verifiable in principle?

  • Examples of moral propositions are, ‘Murder is wrong,’ ‘Intolerance is a vice,’ ‘Humility is a virtue,’ ‘Meat-eating is evil,’ etc.

–       Of course, many philosophers and theologians believe that moral propositions are verifiable propositions. These philosophers are generally called moral realists, or cognitivists.

–                    I.e. they believe that morals are real, not merely expressions of emotion.

–       Utilitarianism and deontology are both types of moral realism, both normative ethics.

–       Ayer also rejects subjectivism.

  • Subjectivism states that an action is morally right, or a thing is good, if it is generally approved of. Therefore a moral proposition is verifiable: is it true or false that it is generally approved of.
    • E.g. “Theft is wrong”
    • I could verify that most people approve that proposition.
    • But that would actually be verifying the proposition, ‘”Theft is wrong” is a belief generally disapproved of.’ –This is not a moral proposition, but a statistical proposition.
    • “Theft is wrong” by itself could not be verified true or false by any observation. It is therefore nonsense.

–       Likewise Utilitarian Propositions, such as “democracy is good”, cannot be verified and are not tautologies; they are therefore meaningless as well.

  • They do not propose facts that can be verified.

–       Ayer makes it clear that he is only concerned with normative, prescriptive, ethical propositions; not descriptive ethical propositions.

  • “x is wrong” could describe the beliefs of a particular society and therefore be a verifiable proposition. Maybe “x is wrong” is not a belief in the society.
  • But if one takes “x is wrong” as a prescription, a normative ethic, it is not verifiable and therefore nonsense.
  • Ayer is therefore concerned with properly refuting normative ethics.

–       Intuitionism is a normative ethic Ayer criticizes.

  • Intuitionism states that we know what is ‘good’ or ‘moral’ or ‘wrong’ because we have a feeling, an intuition, that it is. “I just know it’s wrong”
  • But that is obviously unverifiable because what one persons ‘knows’ to be right may be ‘known’ to be wrong to another person.
    • E.g. the right to an abortion (good or bad?).

–       Furthermore, it is impossible to verify whether one intuition is ‘true’ thereby validating that belief over another with a conflicting belief.

  • I could never verify that my belief – that the right to an abortion is good – is true or false.
  • It is simply a nonsensical proposition.

–       ‘the fundamental ethical concepts are unanalysable, inasmuch as there is no criterion by which one can test the validity of the judgements in which they occur.’ (pp109/110)

–       So the question now emerges as to why we in fact do express prescriptive moral propositions if they are all nonsense.

–       The addition of an ethical word in a proposition adds nothing to its factual content.

  • Thus when one says “You acted wrongly in stealing that money” you are not saying anything more than  “You stole that money”.
  • The word “Wrongly” adds nothing to the proposition in terms of factual content.

–       The addition of the word “wrongly” simply emphasizes one’s disapproval of it.

  • It would be exactly the same as saying “You stole that money” in a peculiar tone of horror, or writing it with many exclamation marks.
  • The tone, or exclamation marks, add nothing to the literal meaning of the sentence.

–       The moral word, the tone, or the exclamation marks serve to show that the expression of it is attended by certain feelings in the speaker/writer.

  • ‘[By saying] “stealing money is wrong,” I produce a sentence which has no factual meaning – that is, expresses no proposition which can be either true or false. It is as if I had written “stealing money!!” … Another man may disagree with me about the wrongness of stealing … but he cannot, strictly speaking, contradict me. For in saying that a certain type of action is right or wrong, I am not making any factual statement … So that there is plainly no sense in asking which of us is in the right. For neither of us is asserting a genuine proposition.’ (pp.110-111)

–       Because a moral proposition is not a factual statement, no morals can be right or wrong. Right and wrong are not things that can be experienced.

–       What is said of the words wrong and right can be applied to every moral word: good, evil, virtue, vice, sin, moral, ought, should, ethical, etc.

–       ‘In every case in which one would commonly be said to be making an ethical judgement, the function of the relevant ethical word is purely “emotive”.’ (p111)

  • Therefore Ayer’s meta-ethics is known as emotivism.

–       Ayer moves on to say that an emotional function is not only to express feeling.

  • Ethical terms also can have the emotional function of arousing feeling, rather than just expressing one’s own.
    • E.g. “It was so evil of him to do that” (“evil” used to arouse anger in other person as well)
  • Moreover, some ethical terms are used in order to command.
    • E.g. “It is your duty to tell the truth” acts as an expression of the command “tell the truth” (Deontology).

–       Indeed, the ethical words we use are used to convey the strength of the command.

  • “You ought to tell the truth” is a less emphatic command.
  • “It is good to tell the truth” is even less emphatic.

–       ‘we may define the meaning of the various ethical words in terms both of the different feelings they are ordinarily to express, and also the different responses which they are calculated to provoke.’ (p111)

–       – One must be careful not to confuse the expression of feeling and the valuative assertion of feeling.

  • It can be verifiable that one actually has a feeling. Therefore this would be a meaningful proposition.
  • But is that feeling cannot be verified to be ‘good’ or ‘bad’, or whatever moral term one chooses.
    • E.g. It is a fact that someone has an aggressive feeling. However, this cannot be factually proved to be good or bad. It may be deemed good in some warrior societies but deemed bad in civilized societies.
    • When Richard Dawkins asserts that we have altruism due to evolution, he makes the erroneous logical leap in positing altruism as therefore being ‘good’. But this is not a proposition that has any meaning. It just reflects his feelings about altruism. We have aggression due to evolution as well – is that therefore necessarily also a ‘good’ thing?! Dawkins uses a hidden morality behind his own.

–       We often feel that our own social morality is superior to others; but this is merely an expression of feeling never fact.

  • ‘We feel that our own system of values is superior … But we cannot bring forward any arguments to show that our system is superior … we finally resort to mere abuse.’     (p. 115)

–       Why we have these differing feelings about our values is a question for psychologists and sociologists, not philosophers.

–       Having said this, Ayer presents a brief psychology of the matter.

  • One of the main causes of moral behaviour is fear (conscious or subconscious).
    • Fear of God, of the law, of the enmity of society, etc.
  • Another cause is a society’s belief in the cause of its own happiness.
    • It encourages behaviour conducive to its believed happiness
    • This is why altruism is recommended in most moral codes, and egotism condemned.

–       However, any proposition that stated altruism to be good, or egotism to be bad, would be committing an error. The propositions could never be verified.

–       All morality is therefore emotions/desires expressed as facts: Emotivism.

–       [I.e. Morality can therefore be seen as a power system, used to control people according to one’s, or a society’s, will.]

  • [cf. Marx, Nietzsche, Weber, Freud, etc]


Critique of Theology (Ch. 6 continued)


–       Ayer continues his chapter by claiming that religious propositions are also insignificant/meaningless/nonsense because they neither can be verified as true or false.

–       He begins this section by refuting Kant’s claim that God can be inferred to exist because of the existence of a world of morals.

  • As morals are not facts, one cannot prove God exists from them.

–       Ayer then refutes the ontological argument by saying that, as an a priori argument, any uncertainty about the premise must be shared by the conclusion, as the latter is deduced solely from the former.

  • Descartes: God is perfect; God is perfect; a perfect being must have existence; therefore God exists.
  • ‘God is perfect’ is unverifiable thus nonsense. Therefore the rest of the argument fails as its basis is withdrawn.

–       Ayer then states that although it is generally acknowledged that the ontological argument fails, many people believe that it is at least possible to prove that God probably, if not definitely, exists.

  • But Ayer says that it is not possible to prove that God probably exists, because the proposition ‘God exists’ is unverifiable. Therefore, there is no probability that this alleged proposition of fact can be verified true.
  • The proposition, ‘Aliens exist,’ is verifiable. We could, in principle discover alien life. Therefore, when people say that aliens probably exist, though we cannot be certain, they are still making a meaningful statement.
  • There is thus a vast difference between the validity of the propositions, ‘God exists’ and ‘Aliens exist’. The latter is verifiable in principle.


–       Ayer moves on to the teleological argument.

  • ‘It is sometimes claimed, indeed, that the existence of a certain regularity in nature constitutes sufficient evidence for the existence of a god.’ (p. 120)
  • This belief is often called creationism, or intelligent design. That, because of the complexities of life, organisms, a God, designer, must exist to have created it.
  • This belief is shared by 45% of the USA’s population (in 2006).
  • But, Ayer indicates that this belief, proposition, is unverifiable. It is verifiable that there is order in nature. But it is not verifiable in principle to prove that an ordered world was designed by a god. Let alone a particular religion’s god.


–       Interestingly, Ayer goes on to say that ’It is important not to confuse this [his] view of religious assertions with the view that is adopted by atheists, or agnostics.’ (p.120)

–       So, it would be wrong to say that logical positivism is necessarily atheistic, even though it claims religious assertions are all nonsense…

–       If the theist’s assertion/proposition that God exists is nonsensical, then the atheist’s assertion, that there is no God, is also nonsensical.

  • God’s existence can neither be proved nor disproved, therefore the atheist’s proposition (there is no God) is also meaningless: what could be used to verify the proposition as true or false? – Nothing.
  • Bertrand Russell acknowledged this fact and subsequently called himself a

‘tea-pot agnostic’:

  • We cannot prove that God does not exist, but neither can we not prove that a tea-pot does not orbit the earth.
  • (Richard Dawkins follows by saying that we cannot prove that the spaghetti monster exists, or that tooth-fairies do not exist. He calls himself a ‘tooth-fairy agnostic’.)

–       Ayer however criticizes agnostics because,

  • “although he refrains from saying either that there is or that there is not a god, he does not deny that the question whether a transcendent god exists is a genuine question. He does not deny that the two sentences ‘There is a transcendent god’ and ‘There is o transcendent god’ express propositions one of which is actually true and the other false … this means that agnosticism is also ruled out.” (p. 121)
  • i.e. An agnostic believes it is possible to one day prove God does or does not exist. Therefore he sits on the fence until that day! Ayer says the proposition is unverifiable in principle and so the agnostic will be sitting there forever.


–       So the beliefs of moralists, theists, atheists and agnostics are all meaningless.

–       Ayer shows that, as with the moralists, their assertions are all expressions of feeling. They do not offer meaningful knowledge about the world, only about their psychological and sociological make-up.

–       Although Ayer says that logical positivism is not atheism, he nonetheless directs his attack against religion. His point is that religion does not give knowledge about the universe, but neither does atheism. In fact, the very name, ‘atheism,’ really means lack of belief, a non-belief rather than a positive new belief.

  • ‘The point which we wish to establish is that there cannot be any transcendent [non-empirical] truths of religion.’(p. 123)


–       But then, Ayer writes, ‘An interesting feature of this conclusion is that it accords with what many theists are accustomed to say themselves. For we are often told that the nature of God is a mystery which transcends the human understanding.’ (p.123/4)

–       Ayer talks about ‘mystical intuition’, a view held by people such as William James, and Swedenborg. That they have mystical experiences about, say, God; but that their experience is unintelligible, incomprehensible: beyond normal understanding and thus indescribable.

  • But, ‘If a mystic admits that the object of his vision is something which cannot be described, then we must also admit that he is bound to talk nonsense when he describes it.’ (p.124)

–       Now, a mystical intuitionist may object that he himself, through his intuition, has verified that his experience is real, and therefore that his assertions are not nonsense, but meaningful.

–       Ayer responds by saying that no-one is denying that the intuitionist has had some unusual ‘mystical’ experience. This can arguably be verified (nowadays) through brain scans, etc. But the man who says that he is seeing God is saying not merely that he is experiencing a religious emotion, but also that there exists a transcendent being who is the object of this emotion. This latter assertion of veridicality cannot be verified, and so is nonsense.

  • Someone may assert that he sees a blue patch and also assert that this seeing corresponds to a real blue patch in the world. So his proposition that the blue patch exists is verifiable.
  • Someone may assert that he sees God and also that this seeing corresponds to a real God that exists. Although the first part may be verifiable, the second is not verifiable.
    • There are two assertions: having a sensation & that the sensation corresponds a to a real object.
  • The point is that although someone may actually have strange mystical visions of God, angels, or whatever; this vision does not prove that it is actually a vision of something real. It could simply be a hallucination, a dream, or a brain malfunction.
  • Nobody contends that the experiences we have in dreams correspond to real things. Someone having a ‘mystical experience’ may as well say that they are having a strong dream.

–       ‘The fact that people have religious experiences is interesting from the psychological point of view, but it does not in any way imply that there is such a thing as religious knowledge, any more than our having moral experiences implies that there is such a thing as moral knowledge.’ (p. 126)



When asked later in life, in 1978, what the main shortcomings of Logical Positivism were, Ayer replied that except for the Emotivism part,

“nearly all of it is false!”

(Ayer on Logical Positivism, Men of Ideas, Bryan Magee. BBC. 1978)



©Peter Sjöstedt-H

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