Fallacy

28 Apriorism: "invincible ignorance"
Closing one's eyes to evidence alleged against something one believes in, such as the honesty of a friend, is frequently described as an attempt to deduce facts from principles, instead of inducing principles from facts. Reasoning a priori, "in advance" of the facts, is regarded as a fallacy. When Galileo invited learned men of his time to view the moons of Jupiter through his telescope, some refused on the grounds that, if they saw anything, it would be an illusion, no doubt diabolical, since the number of the heavenly bodies had already been fixed with finality by astronomy. This is the notorious text-book Let us first consider a rather ordinary case, also related to science.
My friend is ill. Urged to see a doctor, he waves aside the suggestion declaring, "Medicine is an art, not a science. It's a hodgepodge of theory and specific remedies." Now it is true that medicine as a whole is not a science in the sense in which physics as a whole is a science. Yet many medical facts are scientifically established with a reliability approaching that of physics. Diagnosis is frequently very confident and treatment successful. My friend seems to be deducing a distrust of medicine from a definition of "science." The definition of a term cannot affect the nature of the facts; all that one can deduce from a definition of "science" that excludes medicine is that medicine is not a "science" as defined. This has nothing obvious to do with whether or not one should see the doctor.
Yet isn't it likely that what my friend is doing is merely rationalizing a disinclination to seek medical advice? This disinclination may arise from entirely other grounds. But even supposing that he is standing vigorously on principle, what is so wrong with standing on principle? If I refuse to spend an evening watching TV on the principle that TV is a waste of time, I might on a given occasion miss out on a first-class program. Does not that lay me open to a charge of deducing facts from cast-iron principles? Yet a man must be allowed to act on some simplifying principles in his life. My friend avoids medicine as long as he can. I turn my back on TV. My wife refuses to study logic on the principle that it is dull. Her brother refuses to travel on the principle that tourists always get overcharged.
At the worst, some of these principles seem to be merely rather broad and illiberal. As such, arguments based on them can be dismissed as faulty generalizations, rationalizations, or irrelevancies.
The case of the learned men who refused to look at the moons of Jupiter seems more important. What is the nature of their difficulty? The science of astronomy, at that time Ptolemaic and Aristotelian, allowed no provision for the discovery of new planets, and moons are planets. Should the astronomers have overthrown their science at the behest of a crank with a gadget? The telescope had just been invented, and optics was not at all well understood. Nobody in Galileo's day could have provided a very clear explanation of how a telescope works. Cautious men were in effect being asked to invest enormous intellectual capital in what might very well seem a mere conjurer's apparatus. It is rather as if someone were to ask me to invest $1000 in a perpetual motion machine; I do not understand the novel theory of the device, and I don't propose to take the time to learn about it. The analogy is not accurate, for the situation with Galileo is even worse, but it will do. Can I be accused of aphorism when I "deduce" from the laws of classical physics that the machine cannot work? Why not? After all, I am being asked to question these very principles, and I refuse "in advance" to examine the facts.
Whenever in science or ordinary life people predict from principles that something will or will not occur, they are in a sense "deducing" facts in advance. It is hard to see where a line can be drawn between what is called apriorism and ordinary prediction.
There does remain, nonetheless, a cast of mind which seems peculiarly closed to evidence. When confronted with such a mind, one feels helpless, for no amount of evidence seems to be clinching. Frequently the facts are simply ignored or brushed aside as somehow deceptive, and the principles are reaffirmed in unshakable conviction. One seems confronted with what has been called "invincible ignorance." It is this approach to evidence that offends persons with a more empirical cast of mind. Empiricists are characteristically ready to throw out principles that don't fit neatly with the evidence. They regard principles as a posteriori expedients (derived "from after" the facts) rather than absolute charters of truth. Nevertheless, philosophers have spun out many different worlds from such absolute principles. These worlds are often beautiful and compelling, but as they differ among themselves, they cannot all be true, and few have the remotest similarity to the cosmology of modern science.
Our examples are intended to illustrate the cast of mind that clings with blind certainty to principles, even in the teeth of the facts. We do not suppose that there is a use of principle that is apriorist in itself.
EXAMPLE COMMENT
Mrs. Peter is told that a ten-year program of introducing fluoridation into the water supply demonstrates that decay in the teeth of grammar school children fell off 60%, as compared to the school group immediately prior to the introduction of the fluoride. "Well," rejoins Mrs. Peter, "I'm still against the program because I am opposed to experimentation with human beings, children especially." If ever it was sound to generalize that innovations in public health were as apt to be injurious as beneficial to health, this generalization itself would be subject to continual reassessment as man's endeavors to control environment become guided by improved techniques and increased knowledge. Mrs. Peter evidently chooses to reject out of hand such innovations as "experiments." Perhaps her mother objected to vaccination.
"Government regulation is a noose around the neck of initiative, and I'm against having any more of it than we have to. So when the state sets out to prescribe uniform accounting methods for business, I am not even interested in hearing the reasons." The "noose" is the gathering together of a wide range of instances, branding them indiscriminately "GI" for "government interference," and threatening to shoot as a rustler anybody daring to attempt rescuing one calf or another from the corral. "I am not even interested in hearing the reasons." Here speaks the apriorist mind.
A union member addresses a meeting of his local. "Friends and brothers, the object of the company is to make money, and the way to make the most money is to pay low wages. The only way we are going to get any concessions is by fighting for them. The idea of negotiating on a new contract for three weeks more is just so much time wasted. Thank you." Past experience in dealing with the company in question might give more or less support to the speaker's view. But no such evidence is cited; rather the opinion of the company seems to be derived from a general principle concerning employers, that their object is to make money and, hence, to depress wages. Such a speaker is almost impossible to reason with. Down comes the principle, and that settles it. The union member has managed to cast his thought into an unfortunate mold: the cast-iron mold of apriorist principle.

EXAMPLE	COMMENT
Mrs. Peter is told that a ten-year program of introducing fluoridation into the water supply demonstrates that decay in the teeth of grammar school children fell off 60%, as compared to the school group immediately prior to the introduction of the fluoride. "Well," rejoins Mrs. Peter, "I'm still against the program because I am opposed to experimentation with human beings, children especially."	If ever it was sound to generalize that innovations in public health were as apt to be injurious as beneficial to health, this generalization itself would be subject to continual reassessment as man's endeavors to control environment become guided by improved techniques and increased knowledge. Mrs. Peter evidently chooses to reject out of hand such innovations as "experiments." Perhaps her mother objected to vaccination.
"Government regulation is a noose around the neck of initiative, and I'm against having any more of it than we have to. So when the state sets out to prescribe uniform accounting methods for business, I am not even interested in hearing the reasons."	The "noose" is the gathering together of a wide range of instances, branding them indiscriminately "GI" for "government interference," and threatening to shoot as a rustler anybody daring to attempt rescuing one calf or another from the corral. "I am not even interested in hearing the reasons." Here speaks the apriorist mind.
A union member addresses a meeting of his local. "Friends and brothers, the object of the company is to make money, and the way to make the most money is to pay low wages. The only way we are going to get any concessions is by fighting for them. The idea of negotiating on a new contract for three weeks more is just so much time wasted. Thank you."	Past experience in dealing with the company in question might give more or less support to the speaker's view. But no such evidence is cited; rather the opinion of the company seems to be derived from a general principle concerning employers, that their object is to make money and, hence, to depress wages. Such a speaker is almost impossible to reason with. Down comes the principle, and that settles it. The union member has managed to cast his thought into an unfortunate mold: the cast-iron mold of apriorist principle.