I have often found it difficult to explain to someone the difference between theoretical science and the philosophy of a special science. In general, by “someone,” I mean any fairly intelligent human being possessing some modicum of scientific literacy. The problem is not limited to the communication with intellectuals and general academicians, but also non-specialists in more closely related to the field of history and philosophy of science. For instance, a preeminent scholar in the philosophy of biology has often told me that she sees biologists and general philosophers having a difficult time delineating theoretical biology and philosophy of biology; for those trained in a traditional philosophy program, it seems what this scholar does is biology, not philosophy; for those trained in biology, especially in departments that are not very philosophical in their science, what she does is philosophy, not a matter for biologists so much. If demarcation of what a science is has been a problem, then the plight of the historically- and scientifically-knowledgeable philosopher of science is sui generis. I have found explaining the distinction between philosophy of physics and theoretical physics impossible. After all, explaining how discretization of space could have implications for symmetry breaking in the special theory of relativity (STR) is just confusing to the technically-untrained intellectual, because, after all, if it could have an impact on physical explanation, why wouldn’t physicists be interested? Explaining that symmetries in nature are tacitly taken as axiomatic, and that physicists have their own implicit metaphysical assertions when going about their science, is a tall task. Between the scientific technicalities and thorough philosophical subtleties, it is impractical to explain why it is that physicists don’t want to deal with an issue and express why the issue is sufficiently philosophical for it to not be classified as science properly, at least not yet properly science. However, an example of where philosophy of science could make a valuable contribution to pragmatic science, even if the philosophy of science does not make a direct contribution to scientific theory. That is, an example of philosophy of science, in which there is a tangible product in methodology and knowledge, but that does not properly contribute to particulars within scientific, should serve as a satisfactory illustration of the distinction between philosophy of science and science.
The example I have come up with is vitalism in relation to nutrition science. Read any technical book on complex systems, and you will find that “metabolism” pops up in virtually every such text, without fail. A respected scholar at Indiana University Bloomington’s History and Philosophy of Science Department as put it tersely, that “metabolism has proven to be a tough nut to crack.” I have found in philosophical discussion with nutrition expert, Samuel Suska, that defining the term can be quite a difficult task, as in-text discussions of what metabolism is tend to deviate from the original definition, often seeming to include a veritable holism within an organism. Even with, what seems to be, all the salient features of metabolism named and laid out in lists replete with schemas of their interrelations, metabolic processes are still nowhere near entirely understood. If they were, something as simple as why large doses of cinnamon in type-two diabetics improves glucose metabolism —or so it seems, based on studies— would be understood. However, such understanding is not the case; nobody seems to have the slightest clue as to why this might be. It could be the case that, at the end of the day, when everything is truly laid upon the lists, and all schemas exhaustively drawn up, metabolism will be understood. (Please note that no science has ever exhausted the phenomena of Nature, and so this might be a rather far-fetched proposition, this idea of “exhaustion.”) However, this is a metaphysical assumption, and, perhaps, a very important one to the advancement of science: assuming there is a solution to a problem, which is attainable within the approach taken by empirical investigation, is necessary for science to try to resolve the problem within the present framework. That framework, if one were to look up the definition for the word metabolism, is one of chemical understanding of processes; but what if understanding metabolism required something other than chemical descriptions of processes, or, much worse, could not be apprehended by science? Playing devil’s advocate, which isn’t hard in this case, it seems quite possible some underlying metaphysics makes it impossible to explain metabolic processes by the standards and procedures of current scientific programs. What if vitalism is a key component to understanding for those studying nutrition science, and which could act as a guide to that science, but could not shed the type of light that is required by chemistry and biology —or even medicine— to provide knowledge of inner workings requisite to be considered true facts about the natural world.
Vitalism is not something new, but has long been spurned and discarded because of its mystical element that leads the modern scientific mind to view it as far too speculative to be the way the world works. A world in which Nature does not behave in a way that can be grasped by the scientific inquirer is not a reality that the modern scientific mind often readily admits. To be fair, science has largely been able to make do without positing metaphysical entities, at least in the forum of schematic understanding of natural goings-on. However, nutrition science may be the domain in which vitalism might serve the discipline well in understanding how the world works and serve as a pragmatic guide for its experts, being that this science affords the possibility of a much greater holistic treatment of the world, and being that the science is among the more pragmatic professions in science. I will briefly explain how this could be the case. If there is some vital force drives organismic processes, and that more of this vital force would be available in food sources that are closer to their natural form in nature (e.g., not processed or less processed) and, second, living (or foodstuffs not much removed from their living state). At first, this seems a bizarre —“bizarre” to the modern science-minded individual— proposal: nothing has been said about mechanisms, why this might be, or anything of that like, which one might find in a scientific text. Then again, there are some rather remarkable facts about this metaphysical proposal: while no details have been given, there appears to be adequate empirical evidence to judge that this proposal may be correct. For instance, consider every diet out there, keeping in mind that the thermodynamic myth (the calories-in-calories-out theory) is fallacious, having be refuted by such notions as insulin resistance, and one thing becomes clear: they tend to move the individual toward whole foods, even raw whole foods, regardless of the amount of these that’s included. At the very least, they move the consumer away from the more processed foods. Vitalism’s relation to organismic health might work in this way: when sufficiently imbued with the vital force, which is replenished through the consumption of whole and raw foods, an organism optimizes its well-being (e.g., optimal energy levels, psychological health via Spinoza theory of mental health, proper organ function, and digestion). A full philosophy could probably be worked out for nutrition science, which embodies the vitalists’ thinking. The point is that, if this is the way the world is, it is unclear that vitalism provides biochemists, biologists, or medical researchers anything to latch onto to further their respective sciences; yet there seems to be quite a bit to gain for a nutrition expert counseling clients. If anything, proper science might be able to use such a vitalistic principle to inform future research endeavors and adjust methodologies (and perspectives), but such would most assuredly mark another foray into a romantically-inclined science that is reminiscent of the period preceding major discoveries in genetics and the structure of DNA early in the twentieth century.
What this example shows is that a scientifically intractable concept, vitalism, can have every spectral epistemic quality necessary to guide how one thinks within the world —and it is certainly a principle that reflects how Nature might be, in actuality. A philosopher of science could embrace this line of thinking, supposing that studies across a swath of scientific literature sufficiently supports it, but a biochemist, biologist, and medical researcher could not similarly embrace the line of thinking, except insofar as it might guide future research. Very simply stated, science tends to proceed on the basis of detailed explanations, wherein every aspect of the framework, as much as possible, is drawn out. Vitalism, so far as it is currently understood, has nothing to offers detailed scientific accounts of Nature, and remains in the domain of the philosopher…for now, but maybe forever so. The criteria of employing science to develop philosophical theories, as well as the possibility of providing some insightful feedback to the science, is what gives many philosophies of science, straddling science and philosophy, their inherent quality.
 A nice initial reference to vitalism, what it means, etc., is Driesch’s The History and Theory of Vitalism.
 It is worth a mention that even the ethical treatment of animals could play a role in such a philosophy, as the lack of (mental and other) well-being of animals may diminish this vital force.
 Consider romantics involved with this movement, such as Delbrück, Oppenheimer, and Schrödinger, especially What is Life?