What is the power of prediction?

Is the problem the difference in meaning between prediction in science and the popular (that is, ordinary) meaning of prediction? That is the impression I get when the argument turns to the meaning of this word.An example relevant to this message board would be an important prediction made by using the theory of evolution. According to the theory of common descent through small changes, it should be possible to classify the known species in a nested heirarchical pattern. And, indeed, this has been observed -- the species can be classified just as predicted by the theory of evolution.Of course, this classification was known well before Darwin came up with his theories. So this wasn't a prediction in the colloquial sense of something that will be observed in the future. (In fact, I have seen the word retrodiction used for this.)But as far as science goes, it counts as a prediction. The heirarchical classification is not a part of the assumptions that go into the theory of evolution. The theory of evolution was not front loaded with nested heirarchical classification. The nested heirarchy comes out logically and independently from the assumptions that forms the axioms of the theory.But this may be confusing to people who might thing that prediction must refer to phenomena that have not yet been observed (or perhaps not yet recognized).What I am not sure about is the case of Newton and Keplar. Newton formulated his laws of motion and his law of gravity in order to produce Keplar's laws of planetary motion. However, nowhere in the mathematical formulation of Newton's are the orbits of planets explicitly mention; yet, from his laws of motion and the inverse square law of gravity Keplarian orbits can be predicted. Does this count as a prediction of Newton's laws? Or does the fact that Newton formulated them in order to achieve Keplar's laws invalidate this as a prediction?

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"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt

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The problem with this type of argument is that it's possible to construct a theory is such a way that it appears to make this kind of "prediction."

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That is a good point. It is possible that a given theory may be constructed specifically to explain a certain set of facts that are already known.However, I don't think that is the case for the theory of evolution and the nested heirarchical classification of species. I might be wrong, but I don't think the nested hierarchy was foremost in Darwin's thoughts when he developed his theory. I think he was thinking mainly on Malthusian lines. In that case, the nested heirarchical classification would be a bona fide prediction of the theory.Another point that must be made is even if a theory is concocted to explain currently known phenomena (and, of course, that is exactly how theories come to be), it is still an impressive feat; there isn't usually any a priori reason to suppose that any set of phenomena can be explained by a common theory. In the case of evolution, there was no reason to suppose that there could be a idea that explained, say, the biogeographic distribution of species, the laws of heredity, and the nested heirarchy all at once. So, even if the theory of evolution was consciously constructed to explain all these things, it is still quite an impressive achievement (although not as impressive as a true prediction) and should count for something.

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"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt

I don't know if there is a distinction between the two in scientific terminology. I know that I will often use the two words interchangeably.When I do make a distinction between the two (and this is my own idiosyncratic distinction), I think of a prediction as a phenomenon that would cause a problem for evolution if it were not observed, whereas an explanation is a phenomenon that can be explained by evolution if it exists, but would not pose a problem if it is not.The heirarchical classification is a prediction: if the species could not be classified in a unique nested heirarchical pattern, this would be a pretty serious problem.On the other hand, I think the existence of an intelligent species can be explained by means of evolution, but I don't think there is any reason to have expected, simply from the assumptions of common descent through small variations, to expect that intelligent species should exist. (Of course, recognizing that intelligent species do, in fact, exist, one can then make predictions as to what further phenomena should be observed....)However, as I said, these are my own idiosyncratic definitions.

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"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt