The variable X can be any number of things. In typical discourse on the subject it usually stands for the universe, the evolutionary process, humankind, a given animal species, or a particular organ like the eye or a capability like language in humans. X may also stand for the fundamental constants of the universe, like physical constants and physical laws. Sometimes this argument is also based on the anthropic principle that these constants seem tuned specifically to allow intelligent life as we know it to evolve.
While most of the classic forms of this argument are linked to monotheism, some versions of the argument may substitute for God a lesser demiurge, multiple gods and/or goddesses, or perhaps extraterrestrials as cause for natural phenomena, although reapplication of the argument might still imply an ultimate cause. One can also leave the question of the attributes of a hypothesized "designer" completely open, yielding the following simple formulation:
A concise and whimsical teleological argument was offered by G. K. Chesterton in 1908: "So one elephant having a trunk was odd; but all elephants having trunks looked like a plot."
Plato (c. 427–c. 347 B.C.) posited a "demiurge" of supreme wisdom and intelligence as the creator of the cosmos in his work Timaeus. For Plato, the demiurge lacked the supernatural ability to create "ex nihilo" or out of nothing. The demiurge was able only to organize the "ananke" (αναγκη). The ananke was the only other co-existent element or presence in Plato's cosmogony. Plato's teleological perspective is also built upon the analysis of a priori order and structure in the world that he had already presented in The Republic.
Aristotle (c. 384–322 B.C.) also developed the idea of a creator of the cosmos, often referred to as the "Prime Mover" in his work Metaphysics. Aristotle's views have very strong aspects of a teleological argument, specifically that of a prime mover, who (so to speak) looks ahead in setting the cosmos into motion. Indeed, Aristotle argued that all nature reflects inherent purposiveness and direction.
Cicero (c. 106–c. 43 B.C.) also made one of the earliest known teleological arguments. In de Natura Deorum (On the Nature of the Gods) Cicero stated, "The divine power is to be found in a principle of reason that pervades the whole of nature". He was writing from the cultural background of the Roman religion. In Roman mythology the creator goddess, Gaia was borrowed from Greek mythology. The Romans called her Tellus or Terra.
Augustine of Hippo (A.D. 354–430) presented a classic teleological perspective in his work City of God. He describes the "city of man" and essentially posits that God's plan is to replace the city of man with the city of God (at some as-yet-unknown point in the future). Whether this is to happen gradually or suddenly is not made clear in Augustine's work. He did not, however, make a formal argument for the existence of God; rather, God's existence is already presumed and Augustine is giving a proposed view of God's teleology. Augustine's perspective follows from and is built upon the neo-Platonic views of his era, which in turn have their original roots in Plato's cosmogony.
Averroes (Ibn Rushd) was writing on teleological arguments in Moorish Spain from an Islamic perspective in the latter half of the 12th Century, and his influence was very considerable in interpreting many of Aristotle's ideas for the first time in Latin, thereby directly helping to make Aristotle available through a new school of thought known as the Averroists. Averroes was a transitional philosopher, partly a priori neo-Platonic, and partly a posteriori Aristotelian. As a result of his overlapping of the two modes in interpreting Aristotle, and also as a result of what would be known today as a strong disagreement between a deistic and theistic viewpoint in religious circles of that era, Averroes' work was highly controversial and fairly quickly was officially banned in both the Christian and Islamic world. Despite the lingering Platonic influence, Averroes' teleological arguments can be characterized as primarily Aristotelian and presuming one god. He argues based mainly upon Aristotle's Physics, in essence that the combination of order and continual motion in the universe cannot be accidental and requires a Prime Mover, a Supreme Principle, which is in itself pure Intelligence.
The most notable of the scholastics (c. 1100–1500) who put forth teleological arguments was Thomas Aquinas. The translations of Averroist works would set the stage for Aquinas in the 13th century, whose arguments were much more thoroughly Aristotelian, a posteriori and empirically based than his predecessors. Aquinas makes a specific, compact and famous version of the teleological argument, the fifth of his five proofs for the existence of God in his Summa Theologica:
"The fifth way is taken from the governance of the world. We see that things which lack knowledge, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that they achieve their end, not fortuitously, but designedly. Now whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer. Therefore, some intelligent being exists by whom all natural things are directed to their end; and this being we call God."
David Hume, in the mid-18th century, presented arguments both for and against the teleological argument in his Dialogues Concerning Natural Religion. The character Philo, summarizing the teleological argument, uses the example of a watch. Philo is not satisfied with the teleological argument, however. He attempts a number of refutations, including one that arguably foreshadows Darwin's theory. In the end, however, Philo agrees that the teleological argument is valid. Daniel Dennett maintains that, although Hume was ultimately dissatisfied with the teleological argument, his cultural context prevented him from taking any of the alternatives seriously.
The watchmaker analogy, framing the argument with reference to a timepiece, dates back to Cicero, whose illustration was quoted above. It was also used by, among others, Robert Hooke and Voltaire, the latter of whom remarked: "L'univers m'embarrasse, et je ne puis songer Que cet horloge existe, et n'ait point d'horloger (I'm puzzled by the world, I cannot deem, The timepiece real, Its maker but a dream)". Today the analogy is usually associated with the theologian William Paley, who presented the argument in his book Natural Theology published in 1802. As a theology student, Charles Darwin found Paley's arguments compelling; he later developed his theory of evolution in his 1859 book On the Origin of Species by Means of Natural Selection, which puts forward an alternative explanation for complexity in nature.
Many others have countered the watch argument, such as by showing that highly complex systems can be produced by a series of very small randomly-generated steps (see the Weasel program). Richard Dawkins' book The Blind Watchmaker (1986) is one of the best-known examples of this approach outside philosophy and theology.
More recently, proponents of intelligent design have reframed the argument as the concept of irreducible complexity, the premise that certain biological structures can function only if all their substructures are present. This argument asserts that each substructure confers no benefit on its own, and therefore cannot have been selected by an evolutionary mechanism. The argument then posits that the probability of all the substructures being created in a single mutation is too low to be considered possible. Critics describe this as an argument from ignorance that assumes that substructures have not changed in function, and give illustrations of how gradual replacement by a series of advantageous variations can lead to the evolution of structures claimed as being irreducibly complex.
A modern variation of the teleological argument is built upon the anthropic principle. The anthropic principle is derived from the apparent delicate balance of conditions necessary for human life. In this line of reasoning, speculation about the vast, perhaps infinite, range of possible conditions in which life could not exist is compared to the speculated improbability of achieving conditions in which life does exist, and then interpreted as indicating a fine-tuned universe specifically designed so human life is possible. This view is well articulated by John D. Barrow and Frank J. Tipler in The Anthropic Cosmological Principle(1986).
Some of the estimated proportions involved in cosmic "fine-tuning" are remarkable. John Polkinghorne, for instance, pointed out in 1985 that just one factor among many in the cosmos, the difference between expansive and contractive forces in the expanding cosmos according to then-currently accepted theory, depends upon an extremely fine balance of the total energy involved to within one in 1060 , a sixty-one digit number equivalent to taking aim from Earth and hitting an inch-wide target at the farthest reaches of the observable universe. George Wald, also in 1985, wrote in the same context that the conditions for something as fundamental as the atom depend on a balance of forces to within one in 1018. Proponents of the fine-tuned universe form of teleological argument typically argue that taken together, the various fine-tuned balances appear quite improbable, and hint strongly at something designed rather than accidental. And, of course, "designed" implies a "designer" of some kind.
Many highly regarded scientists, mathematicians, philosophers and a few theologians have weighed in on both sides in debate. A counter-argument to the anthropic principle is that one could manipulate statistics to define any number of natural situations that are extremely improbable, but that have happened nevertheless. By the critics' view a key problem in terms of being able to verify whether the hypothesized probabilities are correct, is that the improbable conditions were identified after the event, so they cannot be checked by experiment. And very importantly, there is no ability to sample a large enough set of alternatives (indeed we know of no other cosmos to sample) in order to be able to properly attach any odds or probabilities to these natural situations in the cosmos. Moreover, observations of the cosmos to date indicate that the conditions on Earth are but one of widely varying conditions on many, many planets in many, many star systems, all 228 of which to date do not appear to have met the conditions necessary for life. An analogy from common experience where the odds can be readily calculated is given by John Allen Paulos in Innumeracy: Mathematical Illiteracy and its Consequences (1989), that the probability of a very mundane event such as that of getting any particular hand of thirteen cards in a game of bridge is approximately one in 600 billion. It would be absurd to examine the hand carefully, calculate the odds, and then assert that it must not have been randomly dealt. This perspective on the issue of improbability appears to bolster the position that characteristics of Earth that allow it to sustain life could be just a fortunate and/or accidental "hit", so to speak.
Another variant makes an argument centering on consciousness. Physicist John Wheeler's assertion that the universe seems to require an observer reflects on design not as an external phenomenon, but intrinsic to consciousness. There thus is no search for a criterion of intelligence outside the universe being imposed on it or capable of revealing whether an intelligence has been injected into it; but rather, that consciousness recognizes itself as present in all of existence. Alfred Whitehead had made a similar argument in the early twentieth century. In defense of Whitehead's approach, Charles Hartshorne has written that the panentheism implicit in this argument evades the logical difficulties of the arguments from design of traditional theists. He asks how can a universe that is considered outside of the deity display the design of the being that is outside of? But in Whitehead's view, echoing that of George Berkeley,our very act of what he calls prehension provides us with first-hand evidence of the deity.
In the wake of the "fine-tuned universe" observations and arguments published in the 1980s, the intelligent design movement picked up some of the above concepts, added some additional ones such as irreducible complexity (a variant of the watchmaker analogy) and specified complexity (closely resembling a fine-tuning argument) and attempted to cast the resulting combined form of the teleological argument as scientific rather than speculative. The vast majority of scientists have disagreed with the assertion that it is scientific, as have the findings of a federal court in the United States in a 2005 decision, which ruled that the "intelligent design" arguments are essentially religious in nature. (See Other issues below.)
Proponents of the Intelligent design movement such as Cornelius G. Hunter, have asserted that the methodological naturalism upon which science is based is religious in nature. They commonly refer to it as 'scientific materialism' or as 'methodological materialism' and conflate it with 'metaphysical naturalism'. They use this assertion to support their claim that modern science is atheistic, and contrast it with their preferred approach of a revived natural philosophy which welcomes supernatural explanations for natural phenomena and supports theistic science. This ignores the distinction between science and religion, recognised by both scientists and the clergy, that developed in the centuries since the scientific revolution, that science is obliged to restrict its attention to the natural world, not through any atheistic intent, but because developing a more complete understanding of nature required testing explanations against the natural world.. This viewpoint was encapsulated by Stephen Jay Gould in his concept of Nonoverlapping Magisteria (NOMA),that proposes that science and religion should be considered two compatible, complementary fields, or "magisteria," whose authority does not overlap.
The first (and therefore second) premise assumes that one can infer the existence of intelligent design merely by examining an object. The teleological argument assumes that because life is complex, it must have been designed. It is argued that this is non-sequitur logic. Life or objects are described as "orderly" or "ordered", which implies that an intelligent designer has ordered them. However, in reality, there are examples of systems that are non-random or ordered simply because it is following natural physical processes, for example diamonds or snowflakes.
The design claim is often attacked as an argument from ignorance, since it is often unexplained or unsupported, or explained by unscientific conjecture. Supporters of intelligent design assume that natural objects and man-made objects have similar properties, therefore both must be designed. However, different objects can have similar properties for different reasons, such as stars and light bulbs. Proponents must therefore demonstrate that only intelligent design can cause orderly systems or the argument is invalid.
A designed organism would, on the face of it, be in contradiction to evolutionary theory. As most professional biologists support the theory of biological evolution by means of natural selection, they reject the first premise, arguing that evolution is not only an alternative explanation for the complexity of life but a better explanation with more supporting evidence. Living organisms obey the same physical laws as inanimate objects. A range of chemical reactions could take place, forming other chemicals with complex properties and ways of interacting. Over very long periods of time self-replicating structures could arise and later form DNA. This has in fact been demonstrated artificially via the Avida program, which can construct complex programs without being given any design (similar programs have had similar results with building machines). Thus biologists commonly view the design argument as an unimpressive argument for the existence of a god.
Advocates of design have responded to this objection by pointing out that information theory demonstrates that DNA is a "code," and is therefore not analogous structurally to a snowflake or crystal as the written pages of a book would not be. They also claim that no natural process has ever created a code, and that explanations put forward of the origins of DNA or gradual change are often couched in vague terms such as, for example simply "arising" or "forming" without offering any explanation as to how the thing arose or formed, and that this is unscientific. This argument, however, takes liberties with the definition of "code" and as such, is often considered to be an example of the logical error of equivocation. It may also be the error of reification; i.e., of treating a linguistic metaphor or analogy such as "code" as a real object or state. And it is a fallacy of petitio principii (begging the question), since it assumes the very thing that it concludes: that DNA is not a consequence of a natural process (if it is, then of course it is false that "no natural process has ever created a code"). And it is argumentum ad ignorantiam (argument from ignorance), as it concludes from the lack of a natural explanation for the origin of DNA that there is none, misplacing the burden of proof, which rests with the party who makes the argument (for supernatural origin, in this case).
Another argument states that even if the argument from design proved the existence of a powerful intelligent designer, it would not prove that the designer is God. Voltaire observed:
[F]rom this one argument, I cannot conclude anything more, except that it is probable that an intelligent and superior being has prepared and shaped matter with dexterity; I cannot conclude from this argument alone that this being has made the matter out of nothing or that he is infinite in any sense [i.e. that he is God].
It has also been pointed out that the argument relies on a cultural context of monotheism when it claims to prove the existence of a single, supreme creator Being. In the context of a polytheistic culture, however, the argument could just as easily be used to argue for the existence of gods (in the plural) — a group of intelligent supernatural designers. In David Hume's Dialogues Concerning Natural Religion, the character Philo argued, amidst other counterarguments to the teleological argument, that there "could have been a committee of deities."
Some argue that even if the first and second premises are accepted, the implied designer (Y) might be an unknown force or mere demiurge, not God as God is commonly understood. It is argued in defense that the outside force through which Y came into being might then be explained as a more powerful being resulting in either an omnipotent being or infinite regression.
Critics such as Richard Dawkins often argue that the teleological argument would apply to the designer, arguing any designer must be at least as complex and purposeful as the designed object (in Dawkins' words, "The Ultimate 747", a reference to the probability of a windstorm sweeping through a junkyard and constructing a 747). This, they say, would create the absurdity of an infinite series of designers. However, the counter-argument of an "undesigned designer," akin to Aristotle's uncaused causer, is common. This argument, however, is incomplete as it does not indicate why the designer can be undesigned but the universe cannot.
One version of the argument postulates that the designer does not have any properties that would define him and is singularly simple (yet willful). Creation then happens ex nihilo — not as a cause and effect from the designer (meaning, a change in the creation does not necessitate a change in the Creator, but the Creator certainly is the source of the changes happening in the creation and of the whole creation's existence every second). This doesn't explain, however, why such a designer is better than simply "nothing" out of which everything was born ex nihilo.
The proponents of the argument note that such a designer is not "better" than nothing as far as the above explanation goes. The above version of the argument simply states that the counter-argument of infinite designs is fallacious in the case when the designer itself does not have complex properties or design which would need to be imparted on him by a previous cause. The choice between creatio ex nihilo from literally nothing and from singular yet willful Creator is outside of this argument. If one believes that the Creator must exist (e.g., from teleological, cosmological, ontological or traditional arguments), however, he is not to be stumped by the "infinite designer series" counter-argument in case the said Creator is simple and undifferentiated.
The proponents of the design further argue that it is better because although the designer has no properties which would define or limit him, he has a singular will that is able to bring creation about -- this makes the creation a willful and therefore non-random process infused with purpose. This is expressed by a statement of "He and His Will [or Wisdom] are One". In other words, the designer does not have characteristics that would be separate from him and create a divisiveness within him. As a result, the designer has no need to have an earlier source that would design him (and impart upon him some properties including the property of existence); yet, he is capable of designing and producing the Universe, in which his intelligent design would be visible (or capable of being inferred) because in his essence, ability to create does not exist as a definite force but merely as a possibility which is then instantiated. If such a creation happens constantly (in other words, the world does not exist by itself but constantly depends on the will of its creator to exist), each moment of existence becomes divinely important. (This version of the argument is expressed in many philosophical works of Judaism and is especially accentuated in Kabbalah and stemming from it Chassidism, in particular, Chabad Chassidism.)
Whilst the Universe can at first seem be purposeful and ordered, it has been asserted that upon closer inspection its true function becomes questionable. Scientists such as Richard Dawkins, a high-profile advocate of atheism, reject the claim that the Universe serves any actual function, claiming that the Universe merely 'mimics' purpose. For example, predators appear perfectly 'designed' to catch their prey, whilst their prey seem equally well 'designed' to evade them. Likewise, apparent inconsistencies in the design of organisms have been brought to attention by critics of the teleological argument. Some use such arguments to point towards natural selection as a 'blind' biological designer, as opposed to God.
Proponents of teleology have argued against this objection on various grounds. For example, William A. Dembski says that such arguments are based upon presumptions about what a designer would or would not do, and so constitute a "theological rather than scientific claim." "Not knowing the designer," he continues, they "are in no position to say whether the designer proposed a faulty compromise among those [design] objectives." (Dembski 2004, pp. 58-9)
Additionally, the claim of an apparent inconsistency between the "design" of predators and prey ignores the balance of the ecosystem. Dembski counters, "In criticizing design, [critics] tend to place premium on functionalities of individual organisms and see design as optimal to the degree that those individual functionalities are maximized." But higher-order designs of entire ecosystems might require lower-order designs of individual organisms." (Dembski, 2004, p. 61)
Consider the idea that nature itself is the product of design. How could this be demonstrated? Nature, as we have seen, provides the basis of comparison by which we distinguish between designed objects and natural objects. We are able to infer the presence of design only to the extent that the characteristics of an object differ from natural characteristics. Therefore, to claim that nature as a whole was designed is to destroy the basis by which we differentiate between artifacts and natural objects. Evidences of design are those characteristics not found in nature, so it is impossible to produce evidence of design within the context of nature itself. Only if we first step beyond nature, and establish the existence of a supernatural designer, can we conclude that nature is the result of conscious planning. (p. 268)
For example, it is argued that supernatural events cannot be falsified. There is no empirical (and therefore scientific) way to test for creation per se. To illustrate this, Robert Todd Carroll said "the universe would look the same to us whether it was designed or not." (Going further, scientists such as Richard Dawkins and Victor Stenger have argued at book length that the universe looks as we should expect it to if God does not exist.) This type of argument can be taken as a counterargument to the Intelligent Design version of the teleological argument. Further in this context, natural scientists would say with virtual unanimity that to invoke supernatural explanations does not add to our understanding of the world. Since "supernatural" events are by definition above nature (super-natural), they cannot be considered a scientific alternative to any theory of natural science. (see also: God of the Gaps, Faith and rationality.)
A common question arises that intends on making our theories on the origin of life a matter of subjectivity: "Which is more believable?" or "Which one requires more faith?" Both sides would probably admit that whatever is more believable is not necessarily true. However, if faith is taken to mean a belief that transcends evidence against that belief, belief in evolution is not a matter of faith due to the considerable evidence in its favour. "Which is more believable?" might be considered an irrelevant question as belief is subjective — what is believable for one is unbelievable to another. The question might be rephrased: "if one objectively studies the arguments in favour of intelligent design, and one does the same for the scientific theory of evolution, which one of these theories is more useful and logical as an explanation, and better supported by evidence, and therefore 'most believable'?" (see also: Pascal's wager) But the usefulness of this formulation as a criterion is itself depended on determining what is meant by usefulness. For example, do we consider the moral usefulness of the theory as evidence? Proponents of religion argue for that as part of the whole; opponents find it irrelevant. Is there a first principle by which all can agree on what out to be the criterion for usefulness?
Although intelligent design is often contrasted with evolution, from some religious perspectives there is no inherent contradiction between the two. Certain religious perspectives find nothing illogical about believing in a creator-deity who purposed evolution to propagate the emergence of life on earth. This position is becoming increasingly accepted today — indeed, to illustrate, Pope John Paul II put forward a position of exactly this kind. See also: Evolution and the Roman Catholic Church. Some of the official positions in other religious faiths have agreed with this basic view.