A school of philosophical thought which I believe can be characterised by the statement that only things which are measurable, or which can be derived logically from no assumptions, are real. Or rather, that only with such things does it mean anything to say that they are real. In other words, it is meaningless to claim something as true if its truth or falsity doesn't affect the universe (because anything which affects the universe is, in theory, measurable), unless it is necessarily true or false by logic alone.

This is essentially saying that science and pure logic (including maths) not only are the only ways of discovering truth, but that their limits define when "truth" has any meaning. So in one simple concept, we manage to do away with all those annoying unanswerable questions that have kept amateur philosophers blabbing for so long - such as the existence of a God which does not objectively affect the world, or whether my set of ethics is "better" than yours (unless one is logically inconsistent or makes demonstrably untrue assumptions about the world). It also states, for example, that to ask which of the various mathematically equivalent interpretations1 of quantum mechanics is "true" is meaningless, since they necessarily make the same predictions and so can't be differentiated. This ties in with Karl Popper's ideas of science being about what is "falsifiable".

Of course, you could say it's a bit of a cop out, just rebutting the questions of your opponents by calling them meaningless, and the fundamental acceptance of induction and deduction could also be called into question - but this is a philosophy which has definitely had a great effect on modern scientific thought.

1 - e.g. the Copenhagen interpretation which holds that the wave function is the "ultimate reality", as opposed to interpretations like Bohm's dealing with non-local hidden variables, which as I understand it is mathematically and hence scientifically equivalent, but philosophically quite different (in particular, the Copenhagen version is non-deterministic, while Bohm's is deterministic). See Ooolong's writeup at quantum non-locality for more.

Logical Positivism as a Scientific Model

The positivist model of science predicates itself on the supposition that symbols of mathematical logic are accurate descriptors of cause and effect in the real world. It is a technique which attempted to provide a rational ground for the scientific method and to allow differentiation between science and pseudoscience.

We must remember that mathematical logic as we understand it today was developed only within the last two centuries, from 1870 to 1915, by Frege and Russel. Logical positivism, which originated in a sociological context with Auguste Comte, reigned for a time as a philosophy of science when the formal definitions of the newly-established discipline of mathematical logic was made to serve as a way to provide an intelligible foundation for the scientific method, to grant an authentic and provable reality to scientific truths found through experiment. Because mathematical logic is, like the number itself, essentially a context-free language of pure abstractions, it was perceived at the time as somewhat of a universal panacea.

The attractiveness of formal logic was itself only a step of scientific progress. Expressed in vague intuitions since Heraclitus and the earliest Pre-socratic philosophers of nature known to recorded history, taking form through Renaissance thought, and formalized in Newtonian physics and universal gravitation through mathematics and calculus, the idea of eternal laws of nature, eternal verities of existence, has existed. Indeed, we might consider logical positivism as simply another phase in Western thought's war of mind versus nature, a war towards which even Einstein, bringing us plasticity of space and time, refused to concede his hand to the stupid and blind Gnostic demiourgos - to indeterminacy and unpredictability.

Because it was an atheistic movement, positivism could not take refuge in a transcendent power of deity, so it instead was forced to conceive of the laws of causality as it functioned in the "real" world as simply one application of mathematical logic's symbol set - treating the laws of nature as material conditionals of universal scope ( (∀ x)(Px → Qx) ).

The "material conditional" can be thought of as a statement expressible in terms of an 'if...then' construction. A set of premises phrased as material conditionals is the positivist description of a scientific hypothesis.

The scientific body of knowledge is now to be conceived of as a set of "c-rules". These are expressed as material biconditionals ( (∀ x)(Px ≡ Qx) ). If the set of material conditionals was expressable in terms of the c-rules, the system of premises constuting the hypothesis was science. Otherwise it could be rejected as psuedoscience.

The flaws at this point should be rather obvious. First, what are the "c-rules" but previous Quine-Duhem Thesis which is now accepted as an absolute? This raises an additional question: where do we draw the line between experimentally-derived rules and experimental assumptions? When does experimental result suddenly absolutize itself into scientific law? Doesn't this imply that we can falsify our conclusions if our "c-rules" are not in fact absolutes, but arbitrary constructions which we assume to be true for pragmatic reasons, because we can experimentally duplicate the results?

Perhaps the most philosophically interesting aspect of the logical positivist model of scientific theory is the fact that we are assuming all causality as it occurs in the real world is explicable as a simple deterministic relationship of cause and effect.

The laws of Quantum physics or most any probabilistic model, are quite simply "magic" to positivism's very assumptions! Another problem is the nature of a material biconditional - to fulfill the logical definition in a causal sense means that the relationship must be reversible.

But thermodynamics does not imply for a closed system that a state of greater entropy tends toward a state of less entropy in nature -- in fact, its laws imply quite the opposite. In short, it tells us that there exists a definite linear continuity of time such that the natural tendency of the environment is to gain in entropy and the breaking of structure is non-reversible without artificial intervention -- the shattered glass will not tend to re-form itself!

Are thermodynamics or quantum physics thus to be rejected as spurious pseudosciences?

It would seem that the machinery of the universe is broken...

Or perhaps there is an inherent flaw in any model of reality based on making pragmatic truths into absolutes?!

Remarkably enough, these thoughts have occured to other people, too. Historical answers to these problems of classical positivism are beyond the intended scope of this introductory writeup and form the substance of formal coursework in the Philosophy of Science.

a few courses and 15 minutes glancing through old lecture notes. glad to see my Philosophy minor getting some use!

The verification principle was developed by the Vienna Circle, a group of philosophers who organised themselves in Vienna, Austria, and forms the basis for logical positivism. Its chief proponent, A. J. Ayer, popularised it through his words Language, Truth, and Logic and The Problem of Knowledge, and it forms a comparatively easy-to-grasp principle which can be readily applied to religious language and the problem of meaning in language.

The verification principle is based on the idea that one must be capable of proving a concept for it to be taken seriously; or rather, for it to hold any meaning at all. Assertions must be, in principle, verifiable either through empirical observation, or true of themselves, in order for them to be be meaningful. For example, the statement "All bachelors are men" must be true, for the very definition of a bachelor is an unmarried man. Being true of itself, it is meaningful. If I held up a duck and stated "This is a bird", this would likewise be meaningful, as it can be clearly proven that this is the case.

If we examine religious language, however, then we see how the verification principle can render ideas to be meaningless. The statement "God is love", for example, cannot be empirically proven. God, according to the Judeo-Christian understanding, is taken to be a transcendent being who exists outside the material world. We could never empirically prove His existence, and God or His love are not true of themselves. Therefore, the statement "God is love" is meaningless.

The effect of this renders a great deal of philosophical and ethical thought by the wayside. If these ideas are meaningless, then they are neither true nor false, the Logical Positivists argued, and are not to be taken seriously. With the simple task of determining whether we can empirically prove a statement, much of our previous concepts are rendered wholly redundant.

Logical positivism faced many criticisms. One of those which rose to prominence was Karl Popper's concept of falsification, wherein one should seek ways of proving their ideas wrong in order to justify them. One area in particular in which these two schools of thought differed was with 'positive universal' statements. A good example of one of these would be the statement "all water boils at 100°C". This statement could easily be falsified, by finding water which does not boil at that temperature, but how could one verify it? We could never empirically prove that all water which has ever existed boiled at the same temperature.

Ayer met this point in Language, Truth and Logic, presenting the idea of there being two forms of verification: 'strong' and 'weak'. 'Strong verification' is the same as above, but 'weak verification' differs from this on one key point. If a statement is not verifiable in practice, but is in principle, then Ayer contended that under weak verification it was still meaningful.

Further criticism came from John Hick and Keith Ward. Hick believed that, contrary to the Vienna Circle, religious statements could well be verified - but not in this life. In the afterlife, we would be capable of empirically verifying statements about it, and thus these statements were meaningful as we could eventually verify them. Ward, too, contended that statements such as "God exists" were also verifiable, as there was one being which certainly could verify them - God himself.

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