A standard account of the Copernican revolution might run like this: as the body of celestial observations grew (aided by the invention of the telescope in the early 17th century) anomalies were recorded which revealed inadequacies in the Ptolemaic system, motivating astronomers to consider rival theories. Among these was the heliocentric system of Copernicus, which ultimately turned out to be the best (it explained the data in the simplest, most elegant way, adopted the least auxiliary hypotheses, etc.). Despite the efforts of the Church it gradually came to be accepted. According to this story observation and theory are independent of each other — observation is the neutral party which can topple old theories and adjudicate between new ones.
This presumed independence of theory and observation is one of the main targets in Paul Feyerabend’s Against Method . Feyerabend illustrates his point by considering the tower argument against the motion of the earth, which was for a time one of the main sources of resistance to the heliocentric model of the solar system. He quotes Galileo :
[H]eavy bodies. . . falling down from on high, go by a straight and vertical line to the surface of the earth. This is considered an irrefutable argument for the earth being motionless. For, if it made a diurnal rotation, a tower from whose top a rock was let fall, being carried by the whirling of the earth, would travel many hundreds of yards to the east in the time the rock would consume in its fall, and the rock ought to strike the earth that distance away from the base of the tower.
Needless to say, this argument eventually lost its purchase. Nowadays we understand that the observation that rocks dropped from towers fall perpendicular to the earth is not evidence that the earth is stationary. The force of the reasoning derived from something we have lost :
[Galileo] tells us that the everyday thinking of the time assumes the ‘operative’ character of all motion, or, to use well-known philosophical terms, it assumes a naive realism with respect to motion: except for occasional and unavoidable illusions, apparent motion is identical with real (absolute) motion.
Without absolute motion the tower argument makes little sense, and a crucial component of the Copernican revolution was the adoption by astronomers of Galilean relativity. As the standard story tells it this shift in attitudes toward motion occurred at the level of theory, while the observations — e.g. that falling rocks fall straight to earth — remained stable. Feyerabend disputes this. Naive realism about motion cannot be considered part of the old Ptolemaic theory; one reason is that it is not required, but the more important is that it couldn’t even be stated until Galileo had provided an alternative. Naive realism about motion was not part of the explicit theory, it was an implicit natural interpretation of the observations .
Natural interpretations, unlike explicit hypotheses or postulates, cannot be said to be distinct from the data. On the contrary: they permeate the observation language itself. To put it another way, they are part of what the terms used to state and record observations mean to the people using them. According to Feyerabend, it is not correct to say that in championing Copernicus Galileo was offering a new theory that did a better job of accounting for the data. Quite the opposite: it was inconsistent with the data as then understood. As he writes :
[A] theory may clash with the evidence not because it is not correct, but because the evidence is contaminated.
Galileo did not just argue for a new theory, he provided a new observation language. From this Feyerabend concludes that scientists must from time to time proceed by what he calls ‘counterinduction’, that is by actively developing theories which contradict the current body of observation. By doing so they can unearth (and perhaps then discard) the natural interpretations it contains.
While others have made similar points about holism and the theory-ladenness of observation, Feyerabend is more suspicious than most of overly prescriptive views of scientific method. Taking all this a step further, we can note that his idea that new theories provide not just new explanations of the data, but in effect change the very data to be explained is one that applies to rational discourse in general.
Take materialism and idealism. Idealists have on occasion been accused of denying the existence of their own hands . This criticism likely rings hollow for them — while the idealist does deny that the hand exists in any mind-independent sense, they need not deny the existence of the hand as such, because on their view the things they refer to as their hands were just perceptual entities all along. In virtue of their idealism they mean something different by ‘my hand’.
Similarly, materialism often gets criticised on grounds like “it is the nonsensical idea that mindless physical stuff can crash together to create minds”. The materialist will be unmoved by this, because what is materialism if not the thesis that physical systems can indeed be mindful? As with the above comment on idealism it is at best a cynical rephrasing of the position, and at worst a question-begging criticism of it.
The pattern crops up all over the place, particularly in relation to the big questions of morality, truth, and the existence of God. Beliefs on these topics have deep semantic ripples, and the opportunities for those with differing views to talk past one another are manifold. Feyerabend’s philosophy of science can help us see that this needn’t be because of malice or disinterest on either side, but may simply come down to the fact that charitable interpretation is really hard — it requires more than paying attention to someone’s definitions, it requires stepping into their entire paradigm. The general point can be put somewhat crudely: it is not just the case that the beliefs we hold depend on what we mean by the terms that compose them, but also that what we mean by those terms will depend on (and change with) the beliefs we hold that involve them.
2. Galileo Galilei, Trattato della sfera, quoted AM p50.
3. AM p54.
4. ‘natural interpretation’ is a phrase Feyerabend borrows from Francis Bacon. See AM p55.
5. AM p15.
6. This argument sometimes gets accredited to GE Moore. Presumably this comes from his essay A Defence of Common Sense, though in it he seems to be making a subtler point.