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This is a combination of basically two different questions, but they are interrelated.

My first question is pretty simple. Can we equate falsifiability and meaningfulness? I think at least in the scientific domain, it's true. But what about the overall scenario? Can we say that any statement that is not scientifically falsifiable is not meaningful?

In his "Philosophy of Science: A Very Short Introduction", Samir Okasha gives one example of the failure of falsifiability. Namely when the orbit of Uranus differed significantly from Newtonian prediction. Instead of discarding Newton's theory, people tried to save the theory using an ad hoc that there exists another planet. Eventually, it comes out that indeed there exists another planet that causes that deviation in Uranus' orbit.

Now, does that mean that falsifiability is relative? Can a statement be falsifiable at a time but unfalsifiable at a later time? or vice-versa? Is there any other drawback of falsifiability? And when speaking of falsifiability, does it refers to technical falsifiability or logical falsifiability?

Is there any updated version of it? Namely, in modern physics, there are different branches that are not falsifiable. So how come we can ascribe them the status of 'scientific'?

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  • I think there is a misunderstanding here in your example of Uranus: Even if they decided not to declare the theory false when faced with problematic evidence, the theory remained falsifiable. There just was an additional falsifiable hypothesis made, namely that another planet of a distinctive mass and orbit has to be there. If this had turned out to be false, the theory would have been discarded.
    – Philip Klöcking
    Nov 26 '20 at 21:49
  • Also related philosophy.stackexchange.com/q/22762/3733
    – Dave
    Nov 26 '20 at 22:38
  • @PhilipKlöcking In that particular example, there was just 'one' additional falsifiable hypothesis made. But if they were not to find Neptune(the planet that was causing the deviation) then they would probably make another falsifiable hypothesis. Likewise, people can make an arbitrary number of hypotheses that in fact would ruin the significance of falsifiability.
    – Earman
    Nov 26 '20 at 23:03
  • @Earmen To the contrary, that is how theory-building works for 99% of the time: you try to amend it with additional hypotheses until it is not salvagable anymore or a more general, elegant theory is found of which the former is a special case.
    – Philip Klöcking
    Nov 27 '20 at 12:33
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The philosophy in which falsifiability, or its close relative verifiablilty, is the criterion for meaning is known as logical positivism. It was all the rage in the mid-twentieth century.

The verification principle states that no statement has any meaning unless it is, at least in principle, verifiable.

The problem is that the verification principle is itself a statement and cannot, even in principle, be independently verified. The principle fails its own test and by its own standard is therefore itself meaningless.

Thus, meaning has to be sought elsewhere.

The great proponent of logical positivism was AJ Ayer. You might like to check out his classic text on Language, Truth and Logic.

On the matter raised by Uranus, we may note that even scientists sometimes make mistakes. Newtonian gravity is in principle falsifiable because we can look for cases where it does not apply. This is nicely illustrated by the orbits of Uranus and Mercury. Anomalies in the first proved to be down to Pluto, in the second to Relativistic effects which rendered Newton obsolete.

Some developments in theoretical physics are proving difficult to say whether they are falsifiable or not. String theory is a good example, where almost any fundamental theory of physics can be modelled by modifying the strings to match experimental results. As a consequence, the accusation goes, it is not falsifiable and is therefore metaphysics and not physics. On the other hand string theories to date all assume supersymmetry, and experimental evidence is growing to suggest that reality may not be supersymmetric. So if reality is supersymmetric then string theory may be just metaphysics, but if reality is not supersymmetric then string theory is falisfiable. It is too early to say. Everett's parallel universes provide another example which is probably untestable, while all the many "interpretations" of quantum mechanics have been branded as such because they have all proved so utterly unfalsifiable.

Nevertheless, one cannot deny that these theories have had a profound impact on theoretical physicists - they don't stop to ask whether an idea is falsifiable or not before they start playing with equations, they work out the theory first and worry about the question afterwards.

Falsifiability is therefore not very useful in exploring the frontiers of knowledge, only as a periodic sanity-check on what has been achieved to date.

In science, falsifiability is thus a pragmatic issue; is it conceivable to brew up an experiment to test the statement? This contrasts to falsifiability in philosophy, which is more of a logical issue; is it possible to refute the statement in any way at all?

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  • I am upvoting this answer since it gives an answer to the first question. However, I am not gonna mark this answer as the accepted answer, since the question asks more than what has been answered here (please see the question description to get the full question)
    – Earman
    Nov 26 '20 at 20:58
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    OK, I have added that second discussion. Nov 27 '20 at 5:41

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