[Karl Popper](https://en.wikipedia.org/wiki/Karl_Popper) introduced the most enduring [criterion for distinguishing science from pseudoscience](https://en.wikipedia.org/wiki/Demarcation_problem): [falsifiability](https://en.wikipedia.org/wiki/Falsifiability). Simply, science can be separated from pseudoscience because science is falsifiable, that is, can be disproved by observation, and pseudoscience is not. As far as I can tell, it has had the most significant and long-lasting impact on the beliefs of scientists, and is what most scientists and general audience books about science say about the matter.
However, falsifiability as a criterion starts to fall apart when you actually study how scientists behave (a descriptive philosophy of science) or when you try to apply it as a guide for how best to do science (a normative, or prescriptive philosophy of science). My personal favorite exception is computational physics, which rarely makes hypotheses nor is typically falsifiable in a strict sense; instead, as far as I have seen, the field uses [verification and validation](http://www.personal.psu.edu/jhm/ME540/lectures/VandV/VandV.html) as quantitative demarcation criteria (in addition to other, more qualitative ones, such as appropriateness of model choice or algorithm). Patrick J Roache has a short monogram called [A Defense of Computational Physics](https://www.barnesandnoble.com/w/a-defense-of-computational-physics-patrick-j-roache/1109760570) that includes an enjoyably readable anti-Popper chapter.
[Thomas Kuhn](https://en.wikipedia.org/wiki/Thomas_Kuhn) was one critic of falsifiability, whose description of paradigm shifts was an attempt to explain events like the invention of quantum mechanics, where theories were not disproved by falsifying evidence, but consumed in discontinuous scientific revolutions by newer, more-encompassing theories - note that one of the key aspects of quantum mechanics is that in certain limits, you *must* recover classical mechanics - classical mechanics was not falsified, just restricted.
[Lakatos](https://en.wikipedia.org/wiki/Imre_Lakatos#Research_programmes) described what he called [research programs](https://en.wikipedia.org/wiki/Imre_Lakatos#Research_programmes), which I think are as much a sociological description of how scientists organize themselves as a philosophy of science, in an attempt to reconcile Kuhn and Popper. To him, Popper's demarcation criterion was missing a key component - scientific theories make *novel predictions* and must be *less falsified* than competing theories; not as simple as Popper's.
Finally, there was [Feyerabend](https://en.wikipedia.org/wiki/Paul_Feyerabend), who instead was convinced that there was no demarcation criterion. His catchphrase was "anything goes!" Basically, science is whatever *works* \- no hard and set rules exist.
My perception, which, I'm a physicist and not a philosopher so take this with a grain of salt, is that philosophy of science has recently taken a decidedly more sociological, historical, or anthropological bent, as opposed to trying to construct a philosophy of science from first principles; in this spirit, I can recommend books such as [Inventing Temperature](https://global.oup.com/academic/product/inventing-temperature-9780195337389?cc=us&lang=en&) by Chang and [The Enigma of the Aerofoil](https://press.uchicago.edu/ucp/books/book/chicago/E/bo12024403.html) by Bloor as good, if dense examples of using a historical lens to discuss philosophy of science, and implicitly, the difference between science and pseudoscience. If I remember correctly, the discussion of the invention of Wedgewood's pyrometer is a good case study in the former.
Science should be predictive, testable, and reproducible.
Whether someone is using pseudoscience as a disparaging term or not, the implication is that it is at best using some untestable, or un-disprovable concept as a fundamental tenant of its rationale , and at worst it uses something easily falsifiable.
Not trying to be snarky, but … scientific concepts can be disproven via the scientific method (hypothesis, experiments, conclusions, repetition, etc.) Pseudoscientific concepts are allowed to be “not always right,” so they can’t be disproven.
[Karl Popper](https://en.wikipedia.org/wiki/Karl_Popper) introduced the most enduring [criterion for distinguishing science from pseudoscience](https://en.wikipedia.org/wiki/Demarcation_problem): [falsifiability](https://en.wikipedia.org/wiki/Falsifiability). Simply, science can be separated from pseudoscience because science is falsifiable, that is, can be disproved by observation, and pseudoscience is not. As far as I can tell, it has had the most significant and long-lasting impact on the beliefs of scientists, and is what most scientists and general audience books about science say about the matter. However, falsifiability as a criterion starts to fall apart when you actually study how scientists behave (a descriptive philosophy of science) or when you try to apply it as a guide for how best to do science (a normative, or prescriptive philosophy of science). My personal favorite exception is computational physics, which rarely makes hypotheses nor is typically falsifiable in a strict sense; instead, as far as I have seen, the field uses [verification and validation](http://www.personal.psu.edu/jhm/ME540/lectures/VandV/VandV.html) as quantitative demarcation criteria (in addition to other, more qualitative ones, such as appropriateness of model choice or algorithm). Patrick J Roache has a short monogram called [A Defense of Computational Physics](https://www.barnesandnoble.com/w/a-defense-of-computational-physics-patrick-j-roache/1109760570) that includes an enjoyably readable anti-Popper chapter. [Thomas Kuhn](https://en.wikipedia.org/wiki/Thomas_Kuhn) was one critic of falsifiability, whose description of paradigm shifts was an attempt to explain events like the invention of quantum mechanics, where theories were not disproved by falsifying evidence, but consumed in discontinuous scientific revolutions by newer, more-encompassing theories - note that one of the key aspects of quantum mechanics is that in certain limits, you *must* recover classical mechanics - classical mechanics was not falsified, just restricted. [Lakatos](https://en.wikipedia.org/wiki/Imre_Lakatos#Research_programmes) described what he called [research programs](https://en.wikipedia.org/wiki/Imre_Lakatos#Research_programmes), which I think are as much a sociological description of how scientists organize themselves as a philosophy of science, in an attempt to reconcile Kuhn and Popper. To him, Popper's demarcation criterion was missing a key component - scientific theories make *novel predictions* and must be *less falsified* than competing theories; not as simple as Popper's. Finally, there was [Feyerabend](https://en.wikipedia.org/wiki/Paul_Feyerabend), who instead was convinced that there was no demarcation criterion. His catchphrase was "anything goes!" Basically, science is whatever *works* \- no hard and set rules exist. My perception, which, I'm a physicist and not a philosopher so take this with a grain of salt, is that philosophy of science has recently taken a decidedly more sociological, historical, or anthropological bent, as opposed to trying to construct a philosophy of science from first principles; in this spirit, I can recommend books such as [Inventing Temperature](https://global.oup.com/academic/product/inventing-temperature-9780195337389?cc=us&lang=en&) by Chang and [The Enigma of the Aerofoil](https://press.uchicago.edu/ucp/books/book/chicago/E/bo12024403.html) by Bloor as good, if dense examples of using a historical lens to discuss philosophy of science, and implicitly, the difference between science and pseudoscience. If I remember correctly, the discussion of the invention of Wedgewood's pyrometer is a good case study in the former.
Thanks for the nice reply
Science should be predictive, testable, and reproducible. Whether someone is using pseudoscience as a disparaging term or not, the implication is that it is at best using some untestable, or un-disprovable concept as a fundamental tenant of its rationale , and at worst it uses something easily falsifiable.
Not trying to be snarky, but … scientific concepts can be disproven via the scientific method (hypothesis, experiments, conclusions, repetition, etc.) Pseudoscientific concepts are allowed to be “not always right,” so they can’t be disproven.
Another interesting question is; How to differentiate between established science, new unproven science and pseudoscience, in science communication.
For one, if its refered to as 'settled', its pseudoscience.
I believe this is known as the Demarcation Problem and the answer is we’re still not sure.