Critical Thinking - a Simple and Concise Look 7

 This post is one in a series on the book How to Think about Weird Things: Critical Thinking for a New Age by Theodore Shick, Jr. and Lewis Vaughn. (Fifth Edition)

Unless noted otherwise all quotes used in this series are from that book, usually with the page number noted in parenthesis.

The series should be read in order starting with the first post.

"It is not what the man of science believes that distinguishes him, but how and why he believes it." Bertrand Russell

"SCIENCE AND DOGMA

It's tempting to say that what distinguishes science from all other modes of inquiry is that science takes nothing for granted. But this statement is not strictly true, for there is at least one proposition that must be accepted before any scientific investigation can take place - that the world is publicly understandable. This proposition means at least three things: (1) The world has a determinate structure; (2) we can know that structure; and (3) this knowledge is available to everyone. Let's examine each of these claims in turn.

If the world has no determinate structure - if it were formless and nondescript - it couldn't be understood scientifically because couldn't be explained or predicted. Only where there is an identifiable pattern can there be explanation or prediction. If the world lacked a discernable pattern, it would be beyond our ken. 

But a determinate structure is not enough for scientific understanding, we also need a means of apprehending it. As we've seen, humans possess at least four faculties that put us in touch with the world: perception, introspection, memory, and reason. There may be others, but at present, these are the only ones that have proven themselves to be reliable. They're not 100 percent reliable, but the beauty of the scientific method is that it can determine when they're not. The scientific method is self-correcting, and as a result it is our most reliable guide to the truth." (Page 165)

"What makes scientific understanding public is that the information upon which it is based is, in principle, available to everyone. All people willing to make the appropriate observations can see for themselves whether any particular claim is true. No one has to take anybody's word for anything. To be accepted as true, a scientific claim must be able to withstand the closest scrutiny, for only if it does can we be reasonably sure that it's not mistaken." (Page 166)

"SCIENTIFIC METHODOLOGY

The scientific method is often said to consist of the following four steps:

1. Observe

2. Induce general hypotheses or possible explanations for what we have observed

3. Deduce specific things that must also be true if our hypothesis is true

4. Test the hypothesis by checking out the deduced implications

But this conception of the scientific method provides a misleading picture of scientific inquiry. Scientific investigation can occur only after a hypothesis has been formulated, and induction is not the only way of formulating a hypothesis." (Page 167)

"A moment's reflection reveals that data collection in the absence of a hypothesis has little or no scientific value. Suppose, for example, that one day you decide to become a scientist and having read a standard account of the scientific method, you set out to collect some data. Where would you begin? Should you start by cataloguing all the items in your room, measuring them, weighing them, noting their color and composition, and so on? Should you then take these items apart and catalog their parts in a similar manner? Should you note the relationship of these objects to one another, to the fixtures in the room, to objects outside? Clearly there's enough data in your room to keep you busy for the rest of your life.

From a scientific point of view, collecting this data wouldn't be very useful because it wouldn't help us evaluate any scientific hypotheses. The goal of scientific inquiry is to identify principles that are both explanatory and predictive. Without a hypothesis to guide our investigations, the, there is no guarantee that the information gathered would help us evaluate any scientific hypotheses. The goal of scientific inquiry is to identify principles that are both explanatory and predictive. Without a hypothesis to guide our investigations, there is no guarantee that the information gathered would help us accomplish that goal." (Page 167 - 168)

"Philosopher Karl Popper graphically demonstrated the importance of hypotheses for observation:

Twenty-five years ago I tried to bring home the same point to a group of physics students in Vienna by beginning a lecture with the following instructions: " Take pencil and paper; carefully carefully observe, and write down what you have observed!" They asked, of course, what I wanted them to observe. Clearly the instruction, "Observe!" is absurd. (It is not even idiomatic, unless the object of the transitive verb can be taken as understood.) Observation is always selective. It needs a chosen object, a definite task, an interest, a point of view, a problem." (Page 168)

"Scientific inquiry begins with a problem - why did something occur? How are two or more things related? What is something made of? An observation, of course, is needed to recognize that a problem exists, but any such observation will have been guided by an earlier hypothesis. Hypotheses are needed for scientific observation because they tell us what to look for - they help us to distinguish relevant from irrelevant information.

Scientific hypotheses indicate what will happen if certain conditions are not met. By producing these conditions in the laboratory or observing them in the field, we can assess the credibility of the hypotheses proposed. If the predicted results occur, we have reason to believe that the hypothesis in question is true. If not, we have reason to believe that it's false

Although hypotheses are designed to account for data, they rarely can be derived from data. Contrary to what the traditional account of the scientific method would have us believe, inductive thinking is rarely used to generate hypotheses." (Page 168)

"Hypotheses are created, not discovered, and the process of their creation is just as open-ended as the process of artistic creation. There is no formula for the generating hypotheses. That's not to say that the process of theory construction is irrational, but it is to say that the process is not mechanical. In searching for the best explanation, scientists are guided by certain criteria, such as testability, fruitfulness, scope, simplicity, and conservatism. Fulfilling any one of these criteria, however, is neither a necessary nor A sufficient condition for being a good hypothesis. Science therefore is just as much a product of the imagination as it is of reason.

Even the most beautifully crafted hypotheses, however can turn out to be false. That's why scientists insist on checking all hypotheses against reality. Let's examine how this check might be done in a particular kind of scientific work - medical research.

In medical research, clinical studies offer the strongest and clearest support for any claim that a treatment is effective because they can establish cause and effect beyond a reasonable doubt. Clinical trials allow scientists to control extraneous variables and test one factor at a time. Properly conducted clinical trials have become the gold standard of medical evidence, having proven themselves again and again." (Page 169)

"Finding the occasional straw of truth awash in a great ocean of confusion and bamboozle requires intelligence, vigilance, dedication and courage." Isaac Asimov (Page 172)

"Conducting medical research is exacting work, and many things can go wrong - and often do. Several scientific reviews of medical studies have concluded that a large proportion of published studies are seriously flawed. (In the words of one review: " The mere fact that research reports are published, even in the most prestigious journals, is no guarantee of their quality. " An expert on the medical literature cautions, "the odds are good that the authors [of published clinical research] have arrived at invalid conclusions.") Confounding variables and bias may creep in and skew results. The sample studied may be too small or not representative. The statistical analysis of data may be faulty. In rare cases, the data may even turn out to be faked or massaged. There may be many other detected or undetected inadequacies, and often these problems are serious enough to cripple A study and cast substantial doubt on its conclusions.

To minimize this potential for error, inadequacy or fraud, medical scientists seek replication. Several studies yielding essentially the same results can render A hypothesis more probable than would a lone study. " Two studies seldom have identical sources of error or bias," says epidemiologist Thomas Vogt. "With three or four studies, the chance is even less that the same flaws are shared." Replication means that evidence for or against a certain treatment generally accumulates slowly. Despite the impression often left by the media, medical breakthroughs arising out of a single study are extremely rare.

It should be clear from this sketch of medical research why the scientific method is such an effective means of acquiring knowledge. Knowledge, you will recall, requires the absence of reasonable doubt. By formulating their hypotheses precisely and controlling their observations carefully, scientists attempt to eliminate as many sources of doubt as possible. They can't remove them all, but often they can remove enough of them to give us knowledge.

Not all science can perform controlled experiments, because not all natural phenomena can be controlled. Much as we might like to, there's little we can do about earthquakes, volcanoes , and sinkholes, let alone comets, meteors, and asteroids. So geological and astronomical hypotheses can't usually be tested in the laboratory. They can be tested in the field, however. By looking for the conditions specified in their hypotheses, geologists and astronomers can determine whether the events predicted actually occur.

Since many legitimate sciences don't perform controlled experiments, the scientific method can't be identified with any particular procedure because there are many different ways to assess the credibility of a hypothesis. In general any procedure that serves systematically to eliminate reasonable grounds for doubt can be considered scientific." (Page 172 - 173)

"You don't have to be a scientist to use the scientific method. In fact, many of us use it every day; as biologist Thomas H. Huxley realized, " Science is simply common sense at its best - that is , rigidly accurate in observation, and merciless to fallacy in logic." When getting the right answer is important, we do everything we can to ensure that both our evidence and our explanations are as complete and accurate as possible. In doing so, we are using the scientific method. " (Page 173 - 174)

"Science is organized common sense where many a beautiful theory was killed by an ugly fact." Thomas H. Huxley (Page 174)

"CONFIRMING AND REFUTING HYPOTHESES

The result of scientific inquiry are never final and conclusive but are always provisional and open. No scientific hypothesis can be conclusively confirmed because the possibility of someday finding evidence to the contrary can't be ruled out. Scientific hypotheses always go beyond the information given. They not only explain what has been discovered; they also predict what will be discovered. Since there's no guarantee that these predictions will come true, we can never be absolutely sure that a scientific hypothesis is true.

Just as we can never conclusively confirm a scientific hypothesis, we can never conclusively refute one either. There is a widespread belief that negative results prove a hypothesis false. This belief would be true if predictions followed from individual hypotheses alone, but they don't. Predictions can be derived from a hypothesis only in conjunction wih a background theory. This background theory provides information about the objects under study as well as the apparatus used to study them. If a prediction turns out to be false, we can always save the hypothesis by modifying the background theory." (Page 174)

"It's not true, however, that every hypothesis is as good as every other. Although no amount of evidence logically compels us to reject a hypothesis, maintaining a hypothesis in the face of adverse evidence can be manifestly unreasonable. So even if we cannot conclusively say that a hypothesis is false, we can conclusively say that it's unreasonable." (Page 176)

"A hypothesis threatened by recalcitrant data can often be saved by postulating entities or properties that account for the data. Such a move is legitimate if there's an independent means of verifying their existence. If there is no such means, the hypothesis is ad hoc.

Ad hoc literally means "for this case only." It's not simply that a hypothesis is designed to account for a particular phenomena that makes it ad hoc (if that were the case, all hypotheses would be ad hoc). What makes a hypothesis ad hoc is that it can't be verified independently of the phenomenon it's supposed to explain." (Page 176)

"The real purpose of scientific method is to make sure Nature hasn't misled you into thinking you know something you don't actually know." Robert M. Pirsig (Page 178)

"The moral of this story is to offer a hypothesis to increase our knowledge, there must be some way to test it, for if there isn't, we have no way of telling whether or not the hypothesis is true." (Page 179)

"CRITERIA OF ADEQUACY

To explain something is to offer a hypothesis that helps us understand it. For example, we can explain why a penny left outside turns green by offering the hypothesis that the penny is made out of copper and that when copper oxidizes, it turns green. But for any set of facts, it's possible to devise any number of hypotheses to account for them. Suppose that someone wanted to know what makes fluorescent lights work. One hypothesis is that inside each tube is a little gremlin who creates light (sparks) by striking his pickax against the side of the tube. In addition to the one gremlin hypothesis, there is the two gremlin hypothesis, the three gremlin hypothesis, and so on. Because there is always more than one hypothesis to account for any set of facts and because no set of facts can conclusively confirm or refute any hypothesis, we must appeal to something besides the facts in order to decide which explanation is the best. What we appeal to are criteria of adequacy. As we saw in Chapter 3, these criteria are used in any inference to the best explanation to determine how well a hypothesis accomplishes the goal of increasing our understanding." (Page 179)

"Hypotheses produce understanding by systematizing and unifying our knowledge. They bring order and harmony to facts that may have seemed disjointed and unrelated. The extent to which a hypothesis systematizes and unifies our knowledge is determined by how well it meets the criteria of adequacy. In its search for understanding, science tries to identify those hypotheses that best meet these criteria. As anthropologist Marvin Harris puts it: " The aim of scientific research is to formulate explanatory theories which are (1) predictive (or retrodictive), (2) testable (or falsifiable), (3) parsimonious [simple], (4) of broad scope, and (5) integratable or cumulative within a coherent and expanding corpus of theories." The better a hypothesis meets these criteria, the more understanding it produces. Let's take a closer look at how these criteria work.

Testability

Since science seeks understanding, it's interested only in those hypotheses that can be tested - if a hypothesis can't be tested, there is no way to determine whether it's true or false. Hypotheses, however, can't be tested in isolation, for as we've seen, hypotheses have observable consequences only in the context of a background theory. So to be testable, a hypothesis, in conjunction with a background theory, must predict something more than what is predicted by the background theory alone. If a hypothesis doesn't go beyond the background theory, it doesn't expand our knowledge and hence is scientifically uninteresting.

Take the gremlin hypothesis, for example. To qualify as scientific, there must be some test we can perform - other than turning on the lights - to detect the presence of gremlins. Whether there is such a test will depend on what the hypothesis tells us about gremlins. If it tells us that they are  visible to the naked eye, it can be tested by simply breaking open a fluorescent light and looking for them. If it tells us that they are invisible but sensitive to heat and capable of emitting sounds, it can be tested by putting a fluorescent light in boiling water and listening for tiny screams. But if it tells us that they are incorporeal or so shy that any attempt to detect them makes them disappear, it can't be tested and hence is not scientific.

Scientific hypotheses can be distinguished from nonscientific ones, then, by the following principle:

A hypothesis is scientific only if it is testable, that is, only if it predicts something more than what is predicted by the background theory alone."  (Page 180)

"The gremlin hypothesis predicts that if we turn on a fluorescent light, it will emit light. But this action doesn't mean that the gremlin hypothesis is testable, because the fact that fluorescent lights emit light is what the gremlin hypothesis was introduced to explain. That fact is part of its background theory. To be testable, a hypothesis must make a prediction that goes beyond its background theory. A prediction tells us that if certain conditions are realized, then certain results will be observed. If a prediction can be derived from a hypothesis and its background theory that cannot be derived from its background theory alone, then the hypothesis is testable.

Karl Popper realized long ago that untestable hypotheses cannot legitimately be called scientific. What distinguishes genuine scientific hypotheses from pseudoscientific ones, he claims, is that the former are falsifiable. Although his insight is a good one, it has two shortcomings: First, the term is unfortunate, for no hypothesis is, strictly speaking, falsifiable because it's always possible to maintain a hypothesis in the face of unfavorable evidence by making suitable alterations in the background theory.

The second weakness in Popper's theory is that it doesn't explain why we hold onto some hypotheses in the face of adverse evidence. When new hypotheses are first proposed, there is often a good deal of evidence against them. As philosopher of science Imre Lakatos notes, "When Newton published his Principia, it was common knowledge that it could properly explain even the motion of the moon; in fact lunar motion refuted Newton.... All hypotheses, in this sense, are born refuted and die refuted." Nonetheless, we give credence to some and not others. Popper's theory is hard-pressed to explain why this is so. Recognizing that other criteria play a role in evaluating hypotheses makes sense of this situation." (Page 181 - 182)

"Fruitfulness

One thing that makes some hypotheses attractive even in the face of adverse evidence is that they successfully predict new phenomena and thus open new lines of research. Such hypotheses possess the virtue of fruitfulness. For example, Einstein's theory of relativity predicts that light rays traveling near massive objects will appear to be bent because the space around them is curved. At the same time Einstein proposed his theory, common wisdom was that since light has no mass, light rays travel in Euclidean ststraight lines. To test Einstein's theory, physicist Sir Arthur Eddington mounted an expedition to Africa in 1919 to observe a total eclipse of the sun. If light rays are bent by massive objects he reasoned, then the position of stars whose light passes near the sun should appear to be shifted from their true position. The shift should be detectable by comparing a photograph taken during the eclipse with one taken at night of the same portion of the sky. When Eddington compared the two photographs, he found that stars near the sun during the eclipse did appear to have moved more than those farther away and that the amount of their apparent movement was what Einstein's theory predicted. (Einstein's theory predicted a deflection of 1.75 seconds of arc. Eddington observed a deflection of 1.64 seconds of arc, well within the possible error of measurement.) Thus Einstein's theory had successfully predicted a phenomenon that no one had previously thought existed. In so doing, it expanded the frontiers of our knowledge." (Page 182)

"Other things being equal, the best hypothesis is the one that is the most fruitful, that makes the most successful novel predictions.

If two hypotheses do equally well with regard to all the other criteria of adequacy, the one with greater fruitfulness is better.

Having greater fruitfulness by itself does not necessarily make a hypothesis superior to its rivals, however, because it might not do as well as they do with respect to other criteria of adequacy." (Page 184)

"SCOPE

The scope of a hypothesis - or the amount of diverse phenomena explained and predicted by it is also an important measure of its adequacy: the more a hypothesis explains and predicts, the more it unifies and systematizes our knowledge and the less likely it is to be false. For example, one reason that Einstein's theory of relativity came to be preferred over Newton's theories of gravity and motion is that it had greater scope. It could explain and predict everything that Newton's theories could, as well as some things that  they couldn't. For instance, Einstein's theory could explain a variation in Mercury's orbit, among other phenomena.

It had been known since the middle of the nineteenth century that the planet Mercury's perihelion (the point at which it is closest to the sun) does not remain constant - that the point rotates slowly, or precesses, around the sun at a rate of about 574 seconds of arc per century. Using Newton's laws of motion and gravity, it was possible to account for about 531 seconds of arc of this motion. Leverrier tried to account for the missing 43 seconds of arc in the same way he had accounted for the discrepancies in the orbit of Uranus - by postulating the existence of another planet between Mercury and the sun. He named this planet Vulcan (Star Trek fans take note), but repeated observations failed to find it. Einstein's theory of relativity, however, can account for the precession of Mercury's perihelion without postulating the existence of another planet. According to relativity theory, space is curved around massive objects. Since Mercury is so close to the sun, the space it travels through is more warped (again, Star Trek fans take note) than is the space that the rest of the planets travel through. Using relativity theory, it is possible to calculate the extent to which space is thus bent. It turns out to be just enough to account for the missing 43 seconds of arc in the procession of Mercury's perihelion." (Page 185 - 186)

"For Langevin, Einstein's theory is superior to Newton's because it has greater explanatory and predictive power. The principle he's relying on is this one:

Other things being equal, the best hypothesis is the one that has the greatest scope, that is, that explains and predicts the most diverse phenomena." (Page 186)  

"Simplicity

Interestingly enough, even though considerations of fruitfulness and scope loomed large in the minds of many of those scientists who accepted Einstein's theory, simplicity was what Einstein saw as its main virtue. He wrote, " I do not by any means find the chief significance of the general theory of relativity in the fact that it has predicted a few minute observable facts, but rather in the simplicity of its foundation and in its logical consistency." For Einstein, simplicity is a theoretical virtue par excellence.

Simplicity is notoriously difficult to define. For our purposes, we may say that the simpler of two hypotheses is the one that makes the fewest assumptions. Simplicity is valued for the same reason that scope is - the simpler a theory is, the more it unifies and systematizes our knowledge and the less likely it is to be false because there are fewer ways for it to go wrong." (Page 186 - 187)

"Other things being equal, the best hypothesis is the simplest one, that is, the one that makes the fewest assumptions.

As we've seen, hypotheses often explain phenomena by assuming that certain entities exist. The simplicity criterion tells us that, other things being equal, the fewer such assumptions a theory makes, the better it is. When searching for an explanation, then, it's wise to cleave to the principle known as Occam's Razor (in honor of the medieval philosopher, William of Occam, who formulated it): Do not multiply entities beyond necessity. In other words, assume no more than is required to explain the phenomenon in question. If there's no reason to assume that something exists, it's irrational to do so." (Page 188)

"Conservatism

Since consistency is a necessary condition of knowledge, we should be wary of accepting a hypothesis that conflicts with our background information. As we've seen, not only does accepting such a hypothesis undermine our claim to know; it also requires rejecting the beliefs it conflicts with. If those beliefs are well established, the chances of the new hypothesis being true are not good. In general, then, the more conservative a hypothesis is (that is, the fewer well-established beliefs it conflicts with), the more plausible it is. The criterion of conservatism can be stated as follows:

Other things being equal, the best hypothesis is the one that is the most conservative, that is, the one that fits best with established beliefs.

Things aren't always equal, however. It may be perfectly reasonable to accept a hypothesis that is not conservative provided that it possesses other criteria of adequacy. Unfortunately, there's no foolproof method for determining when conservatism should take a backseat to other criteria.

Indeed, there is no fixed formula for applying any of the criteria of adequacy. We can't quantity how well a hypothesis does with respect to any them, nor can we definitively rank the criteria in order of importance. At times we may rate conservatism more highly than scope, especially if the hypothesis in question is lacking in fruitfulness. At other times we may rate simplicity higher than conservatism more highly than conservatism, especially if the hypothesis has at least as much scope as our existing hypothesis. Choosing between theories is not the purely logical process it is often made out to be. Like judicial decision making, it relies on factors of human judgement that resist formalization.

The process of theory selection, however, is not subjective. There are many distinctions we can't quantify that nevertheless are perfectly objective. We can't say, for example, exactly when day turns into night or when a person with a full head of hair turns bald. Nevertheless, the distinctions between night and day or baldness and hirsuteness are as objective as they come." (Page 189)

"There are certainly borderline cases that reasonable people can disagree about, but there are also clear-cut cases where disagreement would be irrational. It would simply be wrong to believe that a person with a full head of (living) hair is bald. If you persisted in such a belief, you would be irrational. Similarly, it would simply be wrong to believe that the phlogiston theory is a good scientific theory. In general, if someone believes a theory that clearly fails to meet the criteria of adequacy, that person is irrational. " (Page 189 - 190)

"CREATIONISM,EVOLUTION, AND CRITERIA OF ADEQUACY

Criteria of adequacy are what we appeal to when trying to decide which hypothesis best explains a phenomenon. The best hypothesis is the one that explains the phenomenon and meets the criteria of adequacy better than any of its competitors. To make a rational choice among hypotheses, then, it's important to know what these criteria are and how to apply them. Philosopher and historian Thomas Kuhn agrees," It is vitally important," he tells us, "that scientists be taught to value these characteristics and that they be provided with examples that illustrate them in practice." (Page 190)

"In recent years, a number of people (as well as a number of state legislatures) have claimed that the theory of creationism is just as good as the theory of evolution and thus should be given equal time in the classroom. Our discussion of the criteria of adequacy has given us the means to evaluate this claim. If creationism is just as good a theory as evolution, then it should fulfill the criteria of adequacy just as well as evolution does. Let's see if that is the case.

The theory of evolution, although not invented by Darwin, received its most impressive formulation at his hand. In 1859, he published The Origin of Species, in which he argued that the theory of evolution by natural selection provided the best explanation of a number of different phenomena:

It can hardly be supposed that a false theory would explain, in so satisfactory a manner as does the theory of natural selection, the several large classes of facts above specified. It has recently been objected that this is an unsafe method of arguing, but it is a method used in judging of the common events of life, and has often been used by the greatest natural philosophers.

Darwin found that organisms living in isolated habitats (such as islands) have forms related to but distinct from organisms living in neighboring habitats, that there are anatomical resemblances between closely related species, that the embryos of distantly related species resemble one another more than the adults of those species, and that fossils show a distinct progression from the simplest forms to the most complex. The best explanation of these facts, Darwin argued, was that organisms adapt to their environment through a process of natural selection. The hypothesis that all creatures were created by God in one fell swoop, he argued, offers no explanation for these facts.

Darwin realized that many more creatures possess different physical characteristics, and that the characteristics they possess are often inherited from their parents. He reasoned that when an inherited characteristic (like an opposable thumb) increased an organism's chances of living long enough to reproduce, that characteristic would be passed to the next generation. As this process continued, the characteristic would become more prevalent in succeeding generations. This process Darwin called natural selection, which was the driving force behind evolution. Darwin was not aware of the mechanism by which these characteristics were transmitted. The discovery of that mechanism the science of genetics - has further bolstered Darwin's theory, for it has been found that the number of chromosomes and their internal organization is similar among closely related species." (Page 190 - 191)

"A fact is a true statement. A theory is a statement about the way the world is. If the world is the way the theory says it is - if the theory is true - then the theory is a fact. For example, if the Copernican theory of the solar system is true - if planets revolve around the sun - then the Copernican theory is a fact. If Einstein's theory of relativity is true - if E = mc²  - then Einstein's theory of relativity is a fact. Similarly, if the theory of evolution is true, then it's a fact.

So the question arises: when are we justified in believing something to be true? We have already seen the answer: when it provides the best explanation of some phenomena. Biologists consider evolution to be a fact because, in the words of Theodosius Dobzhansky, "Nothing in biology makes sense except in the light of evolution." Evolution is a fact because it's the best theory of how biological change occurs over time.

What often goes unnoticed in these discussions is that every fact is a theory. Take the fact that you're reading a book right now, for example. You're justified in believing that to be a fact because it provides the best explanation of your sense experience. But it's not the only theory that explains your sense experience. After all, you could be dreaming, you could be hallucinating, you could be a brain in a vat, you could be plugged into the matrix, you could be receiving telepathic messages from extraterrestrials, and so on. All of those theories explain your sense experience. You shouldn't accept any of them, however, because none of them is as good an explanation as the ordinary one.

The Intelligent Design theory is on a par with the theory that extraterrestrials are putting thoughts in your head. It's a possible explanation of the evidence, but not a very good one because, like the extraterrestrial theory, it doesn't identify the designer nor does it tell us how the designer did it. Consequently, it doesn't meet the criteria of adequacy as well as the evolutionary theory does. In a court of law, no one would take seriously an explanation of a crime that didn't identify the criminal or how he committed the crime. Similarly, in a science classroom, no one should take seriously an explanation that doesn't identify the cause or how the cause brings about its effect. Evolution does both and does it better than any competing theory. So we're justified in believing it to be true." (Page 195)

"As Plato realized over 2,500 years ago, to say that "God did it" is not to offer an explanation, but to offer an excuse for not having an explanation (Cratylus 426a)." (Page 199)

"We should accept an extraordinary hypothesis only if no ordinary one will do."  (Page 211)

The authors described a problem which I have run into with true believers. They described how parapsychology researchers dismiss research from people who don't believe in psychic abilities. The researchers claim a lack of belief in psychic abilities causes the abilities to fail.

"The ad hoc character of this hypothesis should be obvious. There's no way to test it because no possible data could count against it. Every apparent counterexample can be explained away by appeal to the unconscious. Moreover, accepting it would make the whole field of parapsychology untestable. No unsuccessful experiments could count against the existence of psi because they could simply be the result of experimenter bias. This sort of reasoning convinces many researchers that parapsychology is a pseudoscience." (Page 214)

"Can individually unconvincing studies be collectively convincing? No. What a study lacks in quality cannot be made up in quantity. The evidence generated by questionable studies remains questionable, no matter how many of them there are." (Page 215)

"The amount of understanding produced by a theory is determined by how well it meets the criteria of adequacy: testability (whether it can be tested), fruitfulness (whether it successfully predicts new phenomena), scope (the amount of diverse phenomena explained by it), simplicity (how many assumptions it makes), and conservatism (how well it fits with established beliefs)." (Page 220)