SPECULATION CONTROVERSIES

come to have complete faith in these assertions, indiscrim­inately mixing them up with others that are true and evi­dent.” And in Rule 12, he writes: “If in the series of things to be examined we come across something which our intel­lect is unable to intuit sufficiently well, we must stop at that point, and refrain from the superfluous task of examining the remaining items” Indeed, Descartes' view is consider­ably stronger than “don't speculate” (in the sense of specu­lation I briefly characterized earlier).

Newton, at the end of the Principia, claims to have proved the law of gravity (not with the certainty of mathematical proof, but in his sense of empirically established: “deduced from the phenomena”). He admits, however, that he has “not yet assigned a cause to gravity”—i.e., a reason why the law of gravity holds and has the consequences it does. He says he will not “feign” a hypothesis about this cause, “for whatever is not deduced from the phenomena must be called a hypoth­esis, and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this experimental philosophy, propositions are deduced from the phenomena and are made general by induction.”

Finally, when defenders of this “very conservative” view say “don't speculate,” I will take them to mean at least that scientists should not make public their speculations. Perhaps they would allow scientists to indulge in speculation in pri­vate. (Descartes seems to disallow even that.) But, at a min­imum, scientists should avoid publishing their speculations or communicating them in other ways to the scientific community, an injunction violated by ^omas Young, Lord Kelvin, and string theorists.

b. Moderate

The slogan of this view is a modification of one expressed by President Reagan: “Speculate, but verify.” In the mid­nineteenth century, William Whewell formulated the idea succinctly in this passage: “advances in knowledge are not commonly made without the previous exercise of some bold­ness and license in guessing.”¹¹ In the twentieth century, it was Karl Popper's turn:

According to the view that will be put forward here, the method of critically testing theories and selecting them ac­cording to the results of test, always proceeds on the following lines. From a new idea, put up tentatively, and not yet justi­fied in any way—an anticipation, a hypothesis, a theoretical system, or what you will—conclusions are drawn by means of logical deduction.^{[11] [12]}

The general idea expressed by these and other so-called hypothetico-deductivists, is that the correct scientific proce­dure is to start with a speculation, which is then to be tested by deriving consequences from it, at least some of which can be established, or disproved, experimentally. Even if you do not know that there is evidence for h, you can introduce h into a scientific investigation as a (truth-relevant) spec­ulation, provided you then proceed to test h to determine whether there is evidence that h. The only constraint Popper imposes on the speculation is that it be bold (e.g., speculating that Newton's law of gravity holds for the entire universe, and not just for the solar system). Bolder speculations are easier to test and falsify. According to Whewell, scientists are usually capable of putting forth different speculations to ex­plain a set of phenomena, and this is a good thing: “A facility in devising [different] hypotheses, therefore, is so far from being a fault in the intellectual character of a discoverer, that it is, in truth, a faculty indispensable to his task.”^[13] For these writers there are, then, no constraints on the character of the speculation, other than (for Popper) boldness, and (for Whewell) multiplicity.

The constraints emerge in the testing stage, concerning which Whewell and Popper have significantly different views. Whewell believes that speculative theories can be verified to be true by showing that they exhibit “consili­ence” (they can explain and predict a range of different phe­nomena in addition to the ones that prompted the theories in the first place) and “coherence” (they contain assumptions that fit together, that are not ad-hoc, etc., especially as new assumptions are added when new phenomena are discov­ered). Popper believes that speculative theories cannot be verified, only falsified, by deriving consequences from them that can be tested experimentally and shown to be false. If the speculative theory withstands such attempts to falsify it, all we can claim is that it is well-tested, not that it is verified or true. But, for our purposes, the important claim for both theorists is that speculation is not enough for science. '1 here must be empirical testing. So, in practical terms, we might put it like this: If you want to do science, it is fine, even neces­sary, to speculate. But that must be followed by testing. Don't publish your speculations without at least some progress in testing, even if that amounts only to saying how experiments should be designed.

c. Very Liberal

'lhe slogan here is “Speculate like mad, even if you cannot verify.” 'lhe most famous proponent of this idea is Paul Feyerabend, who proposes adopting a “principle of prolifer­ation: invent and elaborate theories which are inconsistent with the accepted point of view, even if the latter should happen to be highly confirmed and generally accepted..., such a principle would seem to be an essential part of any critical empiricism.”^[14] Feyerabend believes that introducing speculations, particularly ones that are incompatible with accepted theories, is the best way to “test” those theories critically by finding alternative explanations that might be better than those offered by the accepted theories. He places no restrictions on such speculations, other than that they be worked out and taken seriously. On his view, you may, and indeed are encouraged to, publish your speculations even when you have no idea how to test them empirically. Feyerabend would have awarded high marks to Thomas Young, Lord Kelvin, and string theorists for inventing and elaborating speculations about light waves, a mechanical ether, and strings, even if they produced no testable results, or, indeed, even if they produced results incompatible with what are regarded as empirically established facts.^[15]

4.