This is Philosophy of Science. Franz-Peter Griesmaier

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СКАЧАТЬ style="font-size:15px;">      6 Therefore, from 2, 3, and 5, it follows that a piece of white chalk confirms the generalization “All ravens are black.”

      The conclusion stated on line 6 gives rise to the paradox we are worried about. What happens if we replace the confirmation approach by the falsification approach? Somewhat surprisingly, the paradox doesn’t arise. “All nonblack things are nonravens” is falsified by a nonblack thing that is a raven, which is the same as a raven that is not black. Of course, ravens that are not black also falsify the original hypothesis, “All ravens are black.” Thus, the same piece of evidence falsifies the hypothesis in both of its logically equivalent formulations. There is not a whiff of paradox here. To see this more clearly, let’s cast the falsification treatment of the “Raven Paradox” in explicit argument form as well:

       1*. Negative instances falsify a universal generalization, such as the generalization “All ravens are black.”

       2*. Logically equivalent theories are falsified by the same evidence.

       3*. “All ravens are black” is logically equivalent to “All nonblack things are nonravens.”

       4*. A nonblack raven is a negative instance of the generalization “All nonblack things are nonravens.”

       5*. Thus, from 1, it follows that a nonblack raven falsifies the generalization “All nonblack things are nonravens.”

       6*. Therefore, from 2, 3, and 5, it follows that a nonblack raven falsifies the generalization “All ravens are black.”

Line 6* is not paradoxical at all! On the contrary, it is exactly what we would expect on the falsificationist approach. A nonblack raven is a negative instance of the generalization “All ravens are black.” That it falsifies “All ravens are black” follows from 1*. Thus, in light of its ability to avoid the Raven Paradox, while keeping with the view that logically equivalent theories should be evaluated the same in light of the same evidence, the falsificationist approach seems preferable over the confirmation approach to theory acceptance. Again, for the falsificationist, we should accept a theory as long as it hasn’t been falsified, despite rigorous testing. Tests on this view should only be used to rid science of false theories; they are useless for showing that a theory is likely to be true because a test revealed a positive instance.

      It might be tempting to regard the falsificationist treatment of Hempel’s Raven Paradox as a decisive victory for Popper’s approach. It apparently can honor the idea that logically equivalent theories should be treated the same by the same evidence without leading to a paradox. Hempel’s confirmation approach, in contrast, leads to a paradox. However, there are also serious problems besetting Popper’s approach. To see this, let’s return to the spherical earth example from earlier.

      3.2.4 On Flat Earth and Bending Light

      Consider a member of the flat earth society. He believes that the earth is flat. Obviously, he has to defend against the evidence from partially disappearing ships. For if the flat earth theory were true, we expect to observe just continuous shrinking, but not partial disappearance. However, we do observe partial disappearance. It seems that this observation falsifies the flat earth theory decisively. However, the flat earther has a move left, even if it will strike you as some sort of a parlor trick.

      In response to the partially disappearing ship, he might say something along these lines: “Well, this observation is quite compatible with a flat earth. For example, if light didn’t travel in straight lines, but was simply bent slightly toward the earth on its trip from the ship to the observer, then, after a certain distance, the light reflecting off the bottom of the ship would hit the water before it had a chance to reach the eyes of the observer. Thus, the bottom of the ship will disappear from sight before the masts will, even though the earth is flat.”

What this guy is saying sounds outrageous – light being bent? (As we’ll see, it is, as a general idea, not as outrageous as it may first seem, but it couldn’t explain the ship’s partial disappearance.) However, from the perspective of theory falsification, he has a point, namely this one: No hypothesis has observational consequences all by itself. There are always so-called auxiliary hypotheses that need to be in place as well. In our example, the “flat earth” hypothesis together with the claim that light travels in straight lines predict that a ship sailing away from the observer will shrink continuously and uniformly; it will not partially disappear. If the ship does partially disappear, I can blame one of the two claims: either that the earth is flat, or that light travels in straight lines. Either “falsity” would account for the partial disappearance.

      You might still resist this move of blaming an auxiliary hypothesis (in our case, the claim that light travels in straight lines); it might strike you as cheating. But there are many other examples where this move is exactly the move to make. Suppose a group of physics majors gets a result in a lab exercise that contradicts some well-established theory. Clearly, we are not immediately going to overthrow the theory. Rather, we’ll blame the students: They didn’t set up the experiment correctly, they misread the measuring instrument, the instrument was broken, or what have you. The last thing we do is take them to have falsified classical mechanics! If we were to go there, all theories in physics, chemistry, and so on would continuously be falsified by legions of students doing lab exercises in colleges all over the US on a daily basis. Let’s not go there.

The general lesson here is this. Theories and hypotheses always rely on auxiliary hypotheses in order to generate observable predictions. This phenomenon is known as confirmation holism. It was first explicitely discussed by the French physicist Pierre Duhem, who said in his book, The Aim and Structure of Physical Theory: “To seek to separate each of the hypotheses of theoretical physics from the other assumptions upon which this science rests, in order to subject it in isolation to the control of observation, is to pursue a chimera.”² And while Duhem restricted his discussion to physics, it is clear that the underlying point generalizes: If we don’t observe what the main hypothesis predicts, we can blame either the main hypothesis, or one or more of the auxiliary hypotheses. The outcome of the test does not tell us, however, which of the available hypotheses – main or any of the auxiliary ones – we should blame for observed discrepancies. In other words, hypotheses, and especially entire theories, which usually consist of many integrated hypotheses, cannot be conclusively falsified.

      3.3 The Demarcation Problem

To be honest, we have simplified Popper’s position to a considerable extent in order to introduce the notion of falsification. His actual view is much more sophisticated. To see this, consider a famous problem that motivated much of early twentieth-century work in the philosophy of science: the so-called demarcation problem, which is the problem of distinguishing empirical science from various forms of pseudoscience. For a group of philosophers known as logical positivists (a.k.a. logical empiricists), pseudoscience included metaphysics. The positivists sought to draw the distinction in terms of meaningfulness, which in turn was assessed by the verifiability of statements. For example, the statement, “The absolute is beautiful” sounds at first glance meaningful; after all, it is a grammatically well-formed sentence in English. But what exactly does it say? The positivists thought that if a statement has meaning, you should be able to determine whether it is true or false. If you can’t, the statement is meaningless. Now, is it true that the absolute is beautiful? How would you verify it? If you think that this statement can’t be verified, because you don’t know, e.g., where to find the absolute to see whether it is indeed beautiful, then you should conclude, so the positivists contended, that it is meaningless. Of course, you might find the statement evocative, or it might resonate with you on an aesthetic level, and so have some sort of meaning. But what it lacks, according to the positivists, СКАЧАТЬ