PHIL 2100: Introduction to Philosophy
Dr. Robert Lane
Lecture Notes: Friday June 11, 2010


[3.] Philosophy of Religion.



[3.1.] Design Arguments for the Existence of God.


In this chapter Sober examines one sort of argument that has been given to prove that God exists: design arguments.


design argument (df.): an argument that claims that some feature of the world is best explained by postulating the existence of an intelligent designer; this is usually taken to be a single, all-knowing, all-powerful being: God.

·         Design arguments are abductive (i.e., they begin with surprising facts and conclude with a proposed explanation of those facts). Therefore, their conclusions may refer to things that we have not directly observed, like a designer or designers.

·         Because they are abductive, they are constrained by the Surprise Principle and the need to avoid the Only Game in Town Fallacy.


Sober’s chapter 5 opens with a discussion of a design argument put forward by the medieval theologian and philosopher St. Thomas Aquinas (c.1224-1274)—we’re skipping it and going directly to the more modern design arguments.


Sober (p.54) distinguishes between two kinds of design argument:


global design argument (df.): a design argument that cites a general feature of the universe as a whole as a fact that is best explained by an intelligent designer.


local design argument (df.): a design argument that cites a specific feature of the universe as a fact that is best explained by an intelligent designer. [An example is the argument put forward by William Paley…]



[3.1.1] Paley’s Local Design Argument.


In this chapter Sober focuses on a local design argument, one that argues for the existence of God by citing the fact that there exist complex and intricate things that are well-suited to the performance of certain tasks.


The argument that appeals to the existence of such things was formulated by William Paley (1743-1805) in his book Natural Theology (1802).


In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there, I might possibly answer, that, for anything I knew to the contrary, it had lain there forever; nor would it perhaps be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place, I should hardly think of the answer I had before given,—that, for anything I knew, the watch might have always been there. ... [t]here must have existed, at some time, and at some place or other, an artificer or artificers, who formed it for the purpose which we find it actually to answer; who comprehended its construction, and designed its use. (...) (Paley, in Sober pp.120-21)



Paley is describing a surprising observation


O: There is a watch on the beach.


At least two hypotheses present themselves as possible explanations:


H1: The Random Hypothesis: the only thing occurring on the beach is the random action of wind, rain and waves on the sand and grass.


H2: The Design Hypothesis: the watch was designed by an intelligent creator and then left (perhaps lost) on the beach.



According to the Surprise Principle, observation O favors H2 (the Design Hypothesis) over H1 (the Random Hypothesis):



predicts that you’ll find

…and therefore makes the observation of the watch

H1: Random Hypothesis

no watch


H2: Design Hypothesis

a watch



There is one more thing we can rationally infer about the watch: not only was it made by an intelligent designer, it must have been made by a designer of at least human intelligence. Some animals are relatively intelligent—chimpanzees, for example—but it would be enormously surprising if any animal with less than human intelligence had constructed the watch.



[3.1.2.] Paley’s Design Argument.


Paley takes this fictional story of the watch to be analogous to the true story of the existence of living beings, which are also complex things well-suited to a particular task.


On Paley’s view, if the Random Hypothesis is implausible with regard to the watch on the beach, then it is equally implausible with regard to creatures on earth. In both cases, the Surprise Principle says that the relevant observation (the presence of the watch on the beach; the existence of complex living organisms on earth) favors the Design Hypothesis over the Random Hypothesis.


We can best understand Paley’s reasoning as abductive. He first gives an abductive argument about the watch…


O: The watch on the beach is intricate and well suited to the task of measuring time.

If (H2) the watch were created by intelligent design, then O would not be surprising.

H2: the watch was created by intelligent design.


and this argument seems to be strong. He then gives an analogous argument:


O: Living things are intricate and well-suited for the tasks of survival and reproduction.

If (H2) living things were created by intelligent design, then O would not be surprising.

H2: Living things were created by intelligent design.


So Paley gives two arguments (one about a watch, and one about living things) and asserts that the second is at least as strong as the first.


Paley also thought we could infer something about the designer in each case. In the case of the watch, the designer must be pretty intelligent—no ladybug, or chimpanzee, or three-year old human could design such a thing. So just imagine how intelligent the designer of a living creature must be… far more intelligent than a human being.


Again, it is not a flaw that the argument concludes by asserting the existence of something unobserved. Abductive arguments frequently do this. If this were not legitimate, science itself would be radically diminished.



[3.1.2.] Hume’s Criticism of Paley.


David Hume (1711-1776, Scottish) criticized this type of argument in his Dialogues concerning Natural Religion (1779). This is perhaps the best known criticism of the kind of design argument Paley used. (Hume was not criticizing Paley’s version directly—Hume wrote his criticisms years before Paley’s Natural Theology).


However, Sober thinks that Hume’s criticism fails. He thinks this because he thinks that Hume misunderstood local design arguments. Hume thought of them as either inductive arguments or arguments from analogy.


Hume’s criticisms rely on this understanding and, according to Sober, are not very strong, since local design arguments are best understood as abductive.



[] The Design Argument as an Argument from Analogy. 


argument from analogy, a.k.a. analogical argument (df.): a non-deductive argument that depends on a similarity between two things. Because of this similarity, some trait of the first, better-known thing (called the analog) is concluded to be a trait of the second, lesser-known thing (called the target) as well.


Here is an example of an analogical argument:[1]




My VW Jetta handles really well.

Amy’s VW Jetta handles really well.


The degree to which the two cars are similar is the degree to which the inference is justified. We can represent this degree numerically – “n” stands for the degree of similarity, and placing it next to the line (which is a double line, to indicate a non-deductive argument) indicates that the argument is strong to that degree.


Hume criticized Paley’s sort of argument as if it were an argument from analogy, i.e., as if it read as follows:



Watches are the products of intelligent design.

Organisms are the products of intelligent design.


Hume pointed out that n is not very high in this argument. Watches aren’t very similar to living beings, so this argument is relatively weak.


But Sober says that  Paley’s local design argument is best understood not as an argument from analogy but as an abductive argument—an argument to the best explanation. Therefore, it should not be assessed based on the similarity of analog (watches) to target (living organisms), but instead by way of the Surprise Principle. The Surprise Principle says that the Design hypothesis is better warranted than the Random Hypothesis. This claim is not affected by the fact that organisms are dissimilar to other things. So Hume’s criticism misses the mark.



[] The Design Argument as an Inductive Argument.


Having interpreted the local design arguments as arguments from analogy, Hume now considers whether design arguments will be better if interpreted as inductive arguments.


He concludes that, interpreted as inductive arguments, they still fail.


But this criticism of design arguments is not aimed at local design arguments. Instead, Hume is here criticizing global design arguments. Specifically, Hume was criticizing the following argument global design argument:


All the universes we’ve examined up to now have been the product of intelligent design.

Therefore, our universe is the product of intelligent design.


Hume’s criticism is based on the fact that the strength of an inductive argument depends in part on the size of the sample involved.


So the strength of this global design argument is determined in part by the percentage of all universes we’ve examined. So of course this is an incredibly weak argument, since we’ve not examined any universes other than our own. This is about as weak an inductive argument as you can get, which was exactly Hume’s point.


But, again, Sober’s point remains: this is not the correct way to think of Paley’s design argument.


So Hume’s criticisms fail to show that a design argument like the one given by Paley is bad.



[3.1.3.] Has Paley Proved the Existence of God?


According to Sober, Paley’s Design Argument has failed to prove the existence of a single God, such as God is conceived of by Christians, Jews and Muslims. In other words, it fails to prove monotheism:


monotheism (df.): the doctrine that there exists one and only one god.


·         Paley’s argument does not imply the existence of a single creator. Assume that all organisms were made by an intelligent designer. This does not imply that there is one intelligent designer that made all organisms. To think that it does imply this is to commit what Sober calls the Birthday Fallacy:


the birthday fallacy (df.): the mistake in reasoning that occurs when one infers, from the premise that everyone has a birthday, the conclusion that there is a single birthday that everybody has:


Every person has a birthday.

Therefore, there is one birthday that is had by every person.


An analogous, and equally invalid, local design argument would go as follows:


Every organism on earth was created by an intelligent designer.

Therefore, there is one intelligent designer that created every organism on earth.


·         Furthermore, Paley’s argument does not imply anything about what the intelligent designer(s) is like, other than it (they?) is very intelligent. So far as this local design argument is concerned, we may have been designed by a race of super-intelligent aliens.


·         Paley’s argument does establish that the Design Hypothesis is more warranted than the Random Hypothesis. But there are other hypotheses that are in competition with the Design Hypothesis, most especially the theory of evolution.



[3.2.] Evolution and Creationism.


What we have seen so far is that Paley’s local design argument establishes that the Design Hypothesis (H2) is better warranted than the Random Hypothesis (H1). It does not establish that H2 is true, but only that, given the existence of complex and well-adapted living organisms, it is more likely to be true than the H1.


However, there are other hypotheses that, if true, would also explain the existence of complex and well-adapted organisms. One of these is:


H3: Organisms (meaning all present day life on earth) are the result of natural selection.


H3 is one of two ideas that make up the Theory of Darwinian Evolution, a theory that is in conflict with Creationism. In this lecture, we’ll be comparing some arguments for each position.  But first we need a more detailed understanding of each of the two positions…



[3.2.1.] Creationism.


All creationists agree that in order to explain certain characteristics of living organisms, we have to posit an intelligent designer. But there are other things about which creationists disagree:

·         the age of the earth;

·         whether all life on earth traces back to a single common ancestor that was created by God or whether different species were individually created;

·         the number of complex adaptations that require explanation by intelligent design (some think all; some think only a few, e.g. the origin of life itself; consciousness).


So “Creationism” is not a single detailed doctrine that everyone who calls himself or herself a “creationist” agrees about.


To sharpen the idea of creationism, it will help to compare it to its two competitors:


atheistic evolutionism (df.): there is no God; mindless evolutionary processes are responsible for all living beings.


theistic evolutionism (df.): mindless evolutionary processes were set in motion by God, and the current variety of species were created by those processes without any further divine intervention.


creationism (df.): mindless evolutionary processes were set in motion by God, who intervenes in those processes to bring about things that couldn’t otherwise be brought about.

·         On this definition, creationism is silent about many things, e.g., the age of the earth.

·         On this definition, creationism is compatible with the view that some relatively minor changes in living species over time are due to evolutionary processes, such as natural selection. But it maintains that “genuinely novel, complex adaptive features” require direct intervention by a creator.


The presence of a middle position between atheistic evolutionism and creationism indicates that one can be a theist and still believe in evolution. Rejecting creationism does not mean that you do not believe in God. “Current evolutionary theory is neutral on the question of whether there is a God.” (62)



[3.2.2.] Darwin’s Theory of Evolution.


Sober will attempt to show that Darwin’s theory of evolution is better warranted than creationism as an explanation of living organisms.



[] Two Central Claims.


Darwin first put forward his theory of evolution in The Origin of Species (1859). Evolutionary theory has evolved a lot since then, but two basic ideas are still accepted by most biologists:


A. The “Tree of Life”: All present-day life is related. Different types of organism did not come into existence independently; rather, every individual belonging to any species is a part of the same family tree.


This claim is as well established by science as it could be. It is as widely accepted by biologists as Copernicus’ discovery that the earth revolves around the sun is accepted by astronomers.


This claim entails that the different animal species are not fixed and immutable (unchanging). An organism can have a descendent that is very, very different than itself.


But this claim doesn’t say anything about how speciation happens:


speciation (df.): the process whereby one species evolves into another.


It’s the second claim that provides at least a partial explanation of speciation...



B. Natural Selection: evolutionary change resulting from environmental conditions favoring individuals with specific characteristics over others that lack those characteristics.


This is the idea that one species can slowly evolve into another in the following way:

·         There is natural variation of characteristics among the members of a given species. Some individuals are taller, shorter, faster, slower, differently colored, etc., than others. [Darwin didn’t have a very clear idea of how the necessary variation occurs. It was Gregor Mendel’s pioneering work in genetics that filled in the gaps: the required variation is genetic variation.]

·         Because of limited food, predators, and environmental changes, there is a constant competition for survival among the members of a species.

·         Some characteristics will make some individuals better suited to survive than other individuals who lack those characteristics.

·         Because they are more likely to survive, individuals with such characteristics are also more likely to reproduce and pass on their characteristics to later generations.

·         Eventually, those characteristics become more common, because they have been passed on more often.

·         Over a long period of time, as more and more characteristics are passed on in this way within a population, a new species can emerge


Sober uses the following example to illustrate how natural selection can result in a relatively minor change in a population of a single species:


Population of zebras at:

time 1

time 2

time 3


z38   z38   z38




z38   z38   z42


z42   z42   z42

maximum speed: 38 mph

appearance of mutant gene in one organism; it’s max speed is 42 mph

max running speed of all zebras: 42 mph


Zebra42 is better adapted to its environment because it can outrun cheetahs a greater percentage of the time, and it is therefore more likely to have offspring than zebra38­. After several generations, the 42 gene is more prevalent than the 38 gene.


Darwin believed that small changes like the one described above could accumulate, leading to the development of new species, or speciation.

·         For example, suppose that a population of finches is divided… some members fly off on their own, or groups are divided by environmental conditions. The finches wind up on different islands, all in close proximity with one another but with somewhat different environmental conditions. On one island, nuts are plentiful, and on another bugs are, and on still another seeds, and so forth. Through natural selection, the finches on the first island evolve to have beaks suitable for opening nuts, while the second group evolves beaks that are good at grabbing insects, while the third is best adapted to picking seeds. Because of other environmental differences among the islands, body shape and size also differ among the birds. These accumulated differences eventually make the difference between one species of finch and another.



[] How Natural Selection Is, and Is Not, Controversial.


Natural selection is controversial among biologists in two ways:

1.      Not all biologists agree that natural selection was as important in the evolution of different species as Darwin thought. Some believe that natural selection was assisted by other evolutionary mechanisms, which may have played more important roles in producing the tree of life. These scientists think that natural selection is part of the story, but not the whole story.

2.      Even among biologists who believe natural selection was the most important mechanism of evolution, there is uncertainty about whether it could have resulted in certain characteristics of organisms. E.g., sexual reproduction is a mystery from the point of view of natural selection.[2]


How natural selection is not controversial among biologists:

·         What is not controversial is that natural selection did play some role in the evolution of living creatures on earth. There is no serious debate among biologists about whether or not natural selection actually happens.



[] Evolution: Theory or Fact?


·         In 2002, the Cobb County Georgia school board placed stickers on high school biology textbooks, reading: “This textbook contains material on evolution. Evolution is a theory, not a fact, regarding the origin of living things. This material should be approached with an open mind, studied carefully and critically considered.”

·         The school board says it placed the stickers after many parents (they say more than 2000!) complained that the textbook presented evolution as though it were a fact and failed to mention rival theories.

·         The school board was sued by parents and the ACLU (American Civil Liberties Union).

·         In January 2005, a federal judge ruled that Cobb County's stickers are an unconstitutional violation of the separation of church and state. The Cobb County School Board were required to remove the stickers.[3]


There are at least two senses of the word "theory":


theoryS (df): “a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.”[4]


theoryG (df.): “an assumption or guess based on limited information or knowledge.” (American Heritage Dictionary, 2nd College ed.)


The theory of evolution is a theoryS ... and so are the heliocentric theory (the claim that the earth revolves around the sun rather than vice versa), Einstein’s theories of relativity, and numerous other scientific discoveries.


That it is a theoryS does not mean that it lacks strong evidence or confirmation—i.e., it does not mean that it is a theoryG. In fact, the theory of evolution is not a theoryG—it is extremely well supported by the data and theorizing of thousands of different scientists working in a number of different disciplines (biology, paleontology, physical anthropology, etc.). A theoryS that is true accurately represents the facts; and so something can be both a theoryS and a fact.


To say that “Evolution is a theory, not fact” suggests that it does lack strong evidence, that it is a theoryG. But that is not the case—evolutionary theory is supported by a tremendous amount of evidence.



[] Perfectionist Creationism (PC) vs. Darwin’s Theory.


As Sober admits, he does not have room to address every single variety of creationism. He chooses to focus on what I will call


Perfectionist Creationism (PC): “A superintelligent designer fashioned all the complex adaptations we observe organisms to have so that organisms would be perfectly adapted to their environment.” (71; Sober labels it H1)


According to Sober, the Surprise Principle helps to determine whether PC or Evolutionary Theory is a better explanation of the existence of living organisms.


Despite Paley’s claims to the contrary, most species are not “perfectly” adapted to their environments. They are well enough adapted to avoid extinction, at least in the short run, but they are not as well-adapted as they could possibly be.


Consider the panda’s “thumb”:[5]

·         It is not really a finger—just a bone spur protruding from the panda’s wrist.

·         It is constructed from a bone that in other bears is a small part of the wrist (the bone is called the radial sesamoid).

·         The panda’s five actual fingers underlie one paw, while the “thumb” (radial sesamoid) underlies another paw. The two paws are separated by a shallow groove (“furrow”).

·         It is possibly the result of a change in a single gene which caused the radial sesamoid (and the corresponding bone in the ankle) to increase in size, thus forcing the musculature to change to accommodate it.

·         Pandas strip bamboo shoots (the only thing they eat) by running them through the furrow between paws.

·         The panda’s “thumb” is a relatively clumsy device for stripping bamboo, and it wouldn’t be difficult (says Sober) for a omniscient and omnipotent designer to come up with something better.


Consider two hypotheses proposed to explain the panda’s thumb


1.      An omniscient and omnipotent designer created the panda (PC, as applied to panda bears). If this is true, then the structure of the panda’s bone spur is surprising


2.      The panda is descended from carnivorous bears by way of natural selection. If this is true, then the structure of the panda’s bone spur is to be expected, since that bone spur is very similar to a structure on carnivorous bears’ paws.


The Surprise Principle says: (2) is a more likely hypothesis than (1); in argument form:


O: The panda’s thumb is a less-than-perfect tool for slicing bamboo.

If the panda evolved from carnivorous bears, then O would not be surprising.

Therefore, the panda evolved from carnivorous bears.


The argument can be generalized to all animals:


O: Most organisms are not perfectly adapted to their environments; they are adapted only well-enough to avoid extinction in the short-run.

If most organisms evolved by way of natural selection, then O would not be surprising.

Therefore, NS: Most organisms evolved by way of natural selection.


So the fact of imperfect adaptation shows that Evolutionary Theory is a more plausible explanation of the existence of living organisms than PC.


ASIDE: Not all structural similarities indicate descent. Compare the panda’s thumb to the streamlined bodies of sharks and whales. Those body shapes can be explained by the fact that they serve clear functional roles. It is plausible to think that both whales and sharks evolved streamlined bodies – there is no explanatory need to posit a common ancestor. But natural selection alone does not explain the panda’s thumb… thus the need to posit the ancestral link of the panda and the meat-eating bear.[6]



[] More Competing Hypotheses.


But why think that PC is the best form of creationism? Perhaps there is a more modest form that is more plausible than the theory of evolution as an explanation of the organisms we actually find around us.


Here is one candidate (the name is mine, not Sober’s):


Minimal Creationism (MC): “An intelligent designer fashioned all the complex adaptations we observe organisms to have.” (72; Sober labels it H2)


Sober’s criticism: MC makes no predictions one way or the other about what we should expect to find. The theory of evolution predicts (correctly) that we will find lots of imperfect adaptations in nature. PC predicts (incorrectly) that we won’t find any imperfect adaptations. This new version of creationism, MC, doesn’t make either prediction! It says so little that we have no idea what it actually predicts.


We could avoid this problem by revising MC as follows:


Deceptive Creationism (DC): “Organisms did not evolve. Rather, God created each species separately and endowed them with the very characteristics they would have had if they had evolved by natural selection.” (72; Sober labels it H3)

·         “Deceptive Creationism” is my term, not Sober’s. I am calling it this because it resembles the story put forward by some young-earth creationists, that God created the world between 6 and 10 thousand years ago, but Satan has planted evidence (in the form of fossils, different geological strata, dinosaur bones, etc.) to mislead us into thinking that the world is actually much older.


DC does not have the same problem as MC; DC actually does make predictions about what we will observe… the problem is that it predicts exactly the same observations as the theory of evolution by natural selection. In other words, the two theories are predictively equivalent: they predict exactly the same observations.


In this way, DC and evolutionary theory are like the following hypotheses, each of which explains what we are all experiencing when we read out textbooks (Sober 72-73):


J1: “You are now looking at a printed page.”

3: “There is no printed page in front of you, but someone is now systematically misleading you into thinking that there is a printed page in front of you.”


Stopping point for Friday June 11. For next time, read Sober ch.7 (“Can Science Explain Everything?”, pp.76-83) and ch.11 (“The Argument from Evil,” pp.109-116)




[1] I adapt this example from Hurley’s Concise Intro to Logic p.36.

[2] Some researchers believe that sexual reproduction began to develop when bacteria carrying genes from one cell "jumped" into another cell: Lynn Dicks, “Parasitic Invasion Credited with Evolution of Sex,” New Scientist, May 2004, URL =  <>, retrieved June 7, 2010.


[3] (no longer online)


[4] “Science and Creationism: A View from the National Academy of Sciences,” URL = < >


[5] This famous example of less-than-perfect evolutionary adaptation is taken from a well-known essay by Harvard paleontologist Stephen Jay Gould, URL = < >.

[6] The similarity of the streamlined bodies of sharks, whales, and dolphins is an analogous similarity, one that can be explained by their similar behaviors (swimming through water). The wings of insects, birds, and bats is also an analogous similarity.  Similarities among species that are not functionally necessary are homologous similarities. For example, the pentadactyl (five-digit) structure of the limbs of tetrapods (vertebrates with four limbs: amphibians, reptiles, birds, mammals) is not necessary for any behavior shared by all tetrapods. (Ridley, Evolution, pp.45-46) If all tetrapods descended from a common pentadactyl ancestor, then it is not surprising that they all have pentadactyl limbs; if they are were created separately, it is quite surprising that they all have the same limb structure.


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