Observation and Scientific Realism
Positivism, following empiricism, maintained that the real is coterminous with the observable. A scientific theory that posits unobservable entities cannot be taken at face value, but must be regarded as merely instrumentally useful or as plain false. The observable entities are real enough, but the unobservable ones are a species of fiction (no one has observed Sherlock Holmes). There is some irony in this position for a reason strangely neglected: observations are not observable. They ought therefore to be unreal according to the criterion of reality advocated by positivism. An observation is a perceptual occurrence—an impression, as Hume would say—but such occurrences are not themselves perceptible by the senses. No one can see what I experience when I make an observation. You might say that I at least can observe my observation, but that doesn’t make a dent in the underlying point: first, I don’t observe my observation—I merely know about it by introspection; second, such knowledge is private to me and not available to you—you don’t have this kind of knowledge of what I experience. Observation lacks inter-subjectivity in the sense of being a publicly observable occurrence: it is a private occurrence occurring in an individual mind. So the positivists are making something a test of reality that lacks the marks of the real by their own standards.
Observation is a human achievement: what we can observe is constrained by the acuity of our senses, our position in space and time, and our powers of discernment. Is the sun observable? Most of the time it is not, since we can’t stare at it without damaging our eyes. Is it thereby unreal at those times? Does it become real when we don dark glasses? Does a train become unreal as we watch it vanishing into the distance? Of course not: these are just facts about the limits of the human senses. Why would the human senses, confined as they are, impose any limits on what is real? What can you observe with your ears? Sounds, certainly, but can you observe the objects that make these sounds? Not with your ears, but does that mean such objects are not real? Would anyone suppose that the nose is the arbiter of reality? Observation always seems to mean visual observation, but that too is hardly suited to qualify as the measure of reality. The fact is that human vision, like the other senses, is limited in acuity, stimulus bound, prone to illusion, subjectively shaped, modular, and species specific. Why should reality be circumscribed by what is so constituted? Vision may provide our best evidence for what is real, but it can’t be what determinessomething as real; it can’t be the definition of the real.
And what exactly is observation anyway? The OED defines “observe” as “watch attentively”. Note the restriction to the visual sense (we can’t watch with our ears or nose), but the addition of “attentively” is also important. Observing is not simply seeing or even looking; it is doing so while attending to what one is seeing. If you are not attending, or have no power of attention, you cannot be observing. So the positivists must maintain that the test of reality is whether something can be attended to (by humans). But attention is limited, sporadic, and labile—unlike reality. Also attention is more top-down and cognitive than mere seeing: we attend to what we deem important, what we are interested in, what enthralls us. Desire drives attention not merely the perceptual stimulus. Is reality dependent on human desire? Does it care about what interests us? It is a psychological fact about an observer that he or she is watching something attentively; that has nothing to do with whether reality contains a certain type of entity. Is observation necessarily bound up with consciousness? The notion of unconscious observation does not seem oxymoronic, and psychologists have found evidence that it occurs (subliminal perception experiments). Couldn’t a person with blindsight make observations? Then the positivist would have to agree that things exist that cannot be consciously observed. How well does that sit with the empiricism animating their position? Doesn’t it show what a frail reed observation is as a foundation for existence? What if scientists all had blindsight and never consciously observed anything—would the positivist still say that reality is fixed by what they can unconsciously observe? Isn’t that just silly? Why should reality be beholden to the visual system of a certain species with limited powers of sight? Why confuse psychology with physics?
This kind of scientific anti-realism looks completely hopeless.  The point I want to make is that other types of anti-realism are not open to the kinds of objection I have just raised (though they may be implausible on other grounds). For it is glaringly obvious that the existence of unobservable entities is a discovery of science. The microscope, the telescope, and the diffraction chamber greatly expanded our knowledge of the full inventory of the world: microorganisms, remote celestial objects, and invisible atoms (and their parts) became part of accepted reality. Science has discovered that there is more to the world than the unaided human senses can reveal. Moreover, the human senses are themselves objects in the world, with built in limitations, biases, and breakdowns. The picture of the world as extending beyond the reach of the senses is an achievement of science itself. According to science, then, scientific realism is true—at least in the sense that reality is not coterminous (or coeval) with what is (directly) observable by means of the senses. We exist as limited creatures in a larger world not of our own making and containing many things not evident to our senses—things we can’t perceive simply by opening our eyes and looking. But none of this can be said about other areas in which realism and anti-realism have been debated. It is not a theme of morality that moral realism is true. It is not a theorem of mathematics that platonic realism is true. It is not a thesis of psychology that psychological realism is true. It is not a commitment of our ordinary conception of the physical world that idealism is false (Berkeley was right about this, Doctor Johnson was wrong). It isn’t that realism in these areas isn’t a fact about them; rather, realism isn’t a proposition asserted by these areas. Morality may have discovered that slavery is wrong or that animals have rights, but it is not a discovery of morality that moral truths are objectively true independently of human desire or thought. That is a discovery (if it is one) of philosophy. Likewise, the common sense view of the so-called material world is compatible with various kinds of anti-realism about it, which is why we can’t refute idealism by pointing to what common sense has established (or science). Maybe realism is by far the best interpretation of these areas, but it isn’t that they themselves assert its truth. By contrast, we can say that science itself has established that (unaided) observation does not encompass all existing entities. In this sense, realism is internal to science—but external to the other areas mentioned.
The interest of this point is less that science has established scientific realism (in the limited sense defined)—for that seems obvious enough—but rather that other kinds of realism cannot be demonstrated in the same way. It would be bizarre to suggest that morality itself has established that moral values are objective and hence “queer”—as if subjectivism could be ruled out as morally wrong, i.e. contrary to the first-order principles of morality. It is not as if the Ten Commandments contain an extra one stating, “The other commandments are all objectively true”. The moral anti-realist may be an error theorist, but he does not have to be, given that morality asserts of itself that it is objectively true. Moral realism is a metaphysical position not a moral position. So there is no analogue of the role of observation in deciding the question: we haven’t discovered that there are unobservable moral entities in the course of our moral deliberations. There is no moral microscope that has revealed to us a world of values previously unsuspected. And similarly for other areas in which realism has been debated: no discovery within these areas will enable us to settle the question of realism versus anti-realism. This is why we speak of meta-ethics, and could equally speak of meta-psychology, meta-physics, and meta-mathematics.
Here is another way to put the point: it might have turned out that there are no unobservable entities (it is an epistemic contingency that there are), but it couldn’t turn out that moral values are subjective (given that they are actually objective). It is an empirical fact that there are unobservable entities, but it is not an empirical fact that values are objective (given that they are). We didn’t discover empirically that moral realism is true—assuming we did discover that—but rather did so on philosophical grounds, i.e. a priori. By contrast, we did not know a priori that the world contains unobservable entities (microorganisms, atoms, distant galaxies); this we discovered by empirical means. We used science to establish that the world extends beyond the observable. But we didn’t use morality to establish that moral realism is true (for one thing, moral realism is not a moral duty); for that we resorted to philosophy. Thus, given that moral realism is true, it could not have turned out otherwise, whereas scientific realism may have turned out to be false (it is only a contingent fact that some things are not observable). There are worlds “qualitatively identical” to our world that contain no unobservable entities, but there are no worlds “qualitatively identical” to ours in which moral anti-realism is true (similarly for the other kinds of realism).  This is because realism, if true, is true a priori in these areas. It is not an epistemic necessity that microorganisms exist but it is an epistemic necessity that values are objective (assuming they are). Thus scientific realism has a different epistemic status from that of other types of realism.
There is an explanation from within science of the fact that unobservable entities exist, but there is no explanation from within morality of why values are objective (similarly for the external world, psychology, and mathematics). Some entities are simply too small to be seen given the limited acuity of the human eye, and some are too distant: these entities cannot interact with the eye psychophysically. Physics and perceptual psychology explain why we can’t observe certain things. But morality has no explanation for why moral values have objective existence—why they are not reducible to human attitudes. Nor can psychology, as an empirical science, explain why mental states are not reducible to dispositions to behavior (or some such). Nor can common sense concerning tables and chairs explain why material objects are not reducible to sense data. The question of scientific realism, understood as a dispute about the existence of unobservable entities, is not a properly philosophical question, since it can be settled by appeal to the discoveries of science. That is, we know scientifically that there are things in the world that can’t be perceived by the unaided human senses. Of course, there is plenty of room for philosophical debate about the nature of these entities (they might be ideas in the mind of God, say), but it is not a philosophical thesis that some things cannot be perceived. That is simply a scientific truth. But it is not a moral truth that moral values are objective, or a mathematical truth that abstract entities exist, or a truth of psychology that mental states are inner states irreducible to behavior, or a truth of common sense that tables and chairs are distinct from states of mind (“ideas”). Hence there is no analogue of the demonstrable inadequacy of observation to provide a test of reality that can defeat anti-realism in these other areas.
 I am not saying that all types of scientific realism are completely hopeless (though I do believe that), only that the kind that equates the real with the observable is. Clearly the positivists advocated this position in order to save the principle of verifiability not because it looks intrinsically plausible. And there is no limit to human anthropocentrism.