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A teleological or physico-theological argument, also known as an argument from design, or from intelligent design, is an argument for the existence of God, or more generally of some kind of intelligent agent of creation, based upon proposed empirical evidence of human-like design or purpose in nature. The argument goes back to Greek philosophy but is today central to the creationist religious concepts of creation science and intelligent design which are presented as alternative scientific explanations in opposition to evolution theory.
While the concept of an intelligence in the natural order goes back at least to the beginnings of philosophy and science, the concept of a designer of the natural world, or a creating intelligence which has human-like purposes, appears to have begun with Socrates. Plato, his student, and Aristotle, Plato's student, developed differing and complex approaches to the problem, but later classical philosophers such as Plotinus and the Stoics carried on this tradition and developed versions which were eventually accepted into and used by the Abrahamic religions. In the Middle Ages, Islamic theologians such Al Ghazali used arguments from design, although this approach was rejected as unnecessary by literalists, and as unconvincing by many Islamic philosophers. Later, a teleological argument is the fifth of Saint Thomas Aquinas' Five Ways, his rational proofs for the existence of God. In the early 18th century, William Derham published his Physico-Theology, which gave his "demonstration of the being and attributes of God from his works of creation". Later, William Paley, in his 1802 work on natural theology, published a prominent presentation of the design argument with his version of the watchmaker analogy and the first use of the phrase "argument from design".
There have been numerous criticisms of the different versions of the teleological argument. Especially important were the general logical arguments made by David Hume in his Dialogues Concerning Natural Religion, published 1779, and the explanation of biological complexity given in Charles Darwin's Origin of Species, published in 1859.
Since the 1960s, the language of Paley's version of the argument from design has featured prominently in creation science with the claim that this was a scientific alternative to evolutionary theory. The name and strategy of this movement resulted from the fact that when the teaching of evolution was reintroduced into public schools in the United States in the late 1950s, efforts were made to have creationism in the form of "creation science" given equal recognition in school science lessons. After it was ruled in 1987 that this was unconstitutional as teaching one specific religious view, the design argument was reframed as intelligent design which omitted references to God and said it was a "scientific research program". In 2005, a U.S. Federal Court ruled that intelligent design is a religious argument and not science. It was based on negative arguments that complex systems with a supposed appearance of design could not have evolved, but gave no adequate explanation and ignored published scientific explanations of the evolution of this complexity. Intelligent design incorporates aspects of Paley's design argument, but unlike Paley, who was open to deistic design through God-given laws, the intelligent design movement seeks scientific confirmation of repeated miraculous interventions in the history of life.
A "teleological" argument or explanation is one that explains the cause of things or events in terms of the aims, intentions, ends or "designs" (Greek teloi; Latin fines). (The word "design" in these discussions is used in the sense of a "pre-arranged purpose".) Intelligence is implied in any being with plans and designs, and when "intelligent design" is proposed as a cause for anything, this means that something can not have happened purely by chance or "dumb luck" (Greek tuchē).
Such explanations are normal when we explain what caused, for example, a watch to be built or an arrow to be fired at a target, but teleological arguments were once common in the natural sciences also. "Teleological physics" started with Aristotle who introduced the term "final cause" as one of four distinct types of cause into his physics, insisting upon the need to consider "the purpose for which the thing exists or was produced" even concerning events not caused by humans. This type of explanation of nature came under attack by authors such as Francis Bacon in the 1600s, and modern science now avoids such "metaphysical" explanations.
"In medieval philosophy, teleological explanation presupposed a Divine and omniscient designer. Everything operates towards a goal and the goal is predetermined by God." "However, Aristotle mainly applied his final-cause interpretation to living or organic things".
"Aristotle’s view shows that ‘purpose in nature’ need not mean a higher purpose beyond nature. Yet, his immanent purpose does not exclude “higher” purposes, and Aristotelian teleology was pressed into service by medieval thinkers as a framework for understanding God’s agency through nature." In the Christian tradition such arguments have been regularly used by theologians.
The proposal that the order of nature showed evidence of having its own human-like "intelligence" goes back to the origins of western natural philosophy and science, and its attention to the orderliness of nature, often with special reference to the revolving of the heavens. (The Greek word "cosmos" which was introduced in this time means an ordering, and already implies intelligence.) Anaxagoras of Clazomenae, born about 500 BC, is the first person who is definitely known to have explained such a concept using the word "nous" (which is the original Greek term that leads to modern English "intelligence" via its Latin and French translations). Aristotle reports an earlier philosopher from Clazomenae named Hermotimus who had taken a similar position. Amongst Pre-Socratic philosophers before Anaxagoras, other philosophers had proposed a similar intelligent ordering principle causing life and the rotation of the heavens. For example Empedocles, like Hesiod much earlier, described cosmic order and living things as caused by a cosmic version of love, and Pythagoras and Heraclitus, attributed the cosmos with "reason" (logos). In his Philebus 28c Plato has Socrates speak of this as a tradition, saying that "all philosophers agree—whereby they really exalt themselves—that mind (nous) is king of heaven and earth. Perhaps they are right." and later states that the ensuing discussion "confirms the utterances of those who declared of old that mind (nous) always rules the universe". But the proposal of a cosmic intelligence is not yet the same as the concept of a cosmic "designer", with a special relationship to humanity.
Bringing this concept closer to something like a "god", the connection of the word for "design" into these discussions, with the intelligence of nature being compared to a human craftsman, apparently begins with Socrates. His discussions on this and other matters, were reported by his students Plato and Xenophon as well as indirect sources such as Plato's student Aristotle. This is consistent with the fact that both Xenophon and Aristotle remarked specifically that going into the market place and asking questions of craftsmen was a new approach Socrates took to philosophy, in contrast to predecessors, and it is consistent with this then that both Plato and Xenophon use the word demiurge (craftsman) to describe the intelligent being responsible for the natural order. Xenophon's report in his Memorabilia might be the earliest clear account of an argument that there is evidence in nature of intelligent design. The word traditionally translated and discussed as "design" is gnōmē and Socrates is reported by Xenophon to have pressed doubting young men to look at things in the market, and consider whether they could tell which things showed evidence of gnōmē, and which seemed more to be by blind chance, and then to compare this to nature and consider whether it could be by blind chance. In Plato's Phaedo, Socrates is made to say just before dying that his discovery of Anaxagoras' concept of a cosmic nous as the cause of the order of things, was an important turning point for him. But he also expressed disagreement with Anaxagoras' understanding of the implications of his own doctrine, because of Anaxagoras' materialist understanding of causation. Socrates complained that Anaxagoras restricted the work of the cosmic nous to the beginning, as if it were uninterested and all events since then just happened because of causes like air and water. Socrates, on the other hand, apparently insisted that the demiurge must be "loving", particularly concerning humanity. (In this desire to go beyond Anaxagoras and make the cosmic nous a more active manager, Socrates was apparently preceded by Diogenes of Apollonia.) In the Phaedo, Socrates seems to suggest that he also failed to develop a fully satisfactory teleological account of the active and loving ordering of nature by an intelligent design.
Plato (c. 427 – c. 347 BC) has a character explain the concept of a "demiurge" with supreme wisdom and intelligence as the creator of the cosmos in his work Timaeus. 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. Plato does not propose creation ex nihilo; rather, the demiurge made order from the chaos of the cosmos, imitating the eternal Forms.
Plato's world of eternal and unchanging Forms, imperfectly represented in matter by a divine Artisan, contrasts sharply with the various mechanistic Weltanschauungen, of which atomism was, by the 4th century at least, the most prominent... This debate was to persist throughout the ancient world. Atomistic mechanism got a shot in the arm from Epicurus... while the Stoics adopted a divine teleology... The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or inject intelligence into the system. This was how Aristotle (384–322 bc), when still a young acolyte of Plato, saw matters. Cicero (On the Nature of the Gods 2. 95 = Fr. 12) preserves Aristotle's own cave-image: if troglodytes were brought on a sudden into the upper world, they would immediately suppose it to have been intelligently arranged. But Aristotle grew to abandon this view; although he believes in a divine being, the Prime Mover is not the efficient cause of action in the Universe, and plays no part in constructing or arranging it... But, although he rejects the divine Artificer, Aristotle does not resort to a pure mechanism of random forces. Instead he seeks to find a middle way between the two positions, one which relies heavily on the notion of Nature, or phusis.
— R. J. Hankinson, Cause and Explanation in Ancient Greek Thought
Aristotle (c. 384 – 322 BC) argued that the most complete explanation in regard to the natural, as well as the artificial, is for the most part teleological. Based solely on the study of immature specimens, for example, one wouldn't feel confident in one's knowledge of the species. Similarly, knowledge of what use an animal makes of a feature is crucial to understanding it (for example, that birds use wings for flight). Aristotle did not believe nature is endowed with the same rational purpose and direction as human activity and artifacts. However, he did believe that the adult form is present in the offspring, having been copied from the parent, and that the parts of an organism are good for their purpose. He maintained that by an imperfect but compelling analogy, one could almost say they're purpose built to suit their essential function. Furthermore, knowledge of that function or end-purpose is essential because any other aitia, or explanations one could offer for the organ, would be tremendously informed given the telos.
In his Metaphysics, Aristotle addressed the existence of gods. Rather than envisioning an Artificer as Plato did, he believed that the eternal cosmos required no creation. Aristotle argued for the existence of one or more unmoved movers to serve as nature's role models and constant inspiration (see Prime Mover and Daimon). Aristotle described the movers as immaterial "active intellects", incapable of perceiving or interacting with the cosmos, thus assuredly "unmoved". To the extent permitted by the vagrancies of matter, he believed the natural pleroma is exerting its full potential, because it has had an eternity in which to do so. This is not to imply a naïve, panglossian idealism, but a logically valid argument from a natural scientist who took a great deal of interest in efficient causal analyses. As a more unsettled account of the species, he briefly recounted survival of the fittest, well known even in Aristotle's time. It would have been infinitely long ago, he argued, and thus would have remained effectively unchanged for an infinitely long duration. Conceding that monstrosities come about by chance, he disagrees with those who, like Democritus, ascribe all nature purely to chance because he believes science can only provide a general account of that which is normal, "always, or for the most part".
Cicero (c. 106 – c. 43 BC) presented an early teleological argument in De Natura Deorum (On the Nature of the Gods), arguing that divine power can be found in reason, which exists throughout nature. He developed an early version of the watchmaker analogy, which was later developed by William Paley.
"When you see a sundial or a water-clock, you see that it tells the time by design and not by chance. How then can you imagine that the universe as a whole is devoid of purpose and intelligence, when it embraces everything, including these artifacts themselves and their artificers?"—Cicero, De Natura Deorum, ii. 34
As an appeal to general revelation, Paul the Apostle (AD 5-67), argues in Romans 1:18-20, that because it has been made plain to all from what has been created in the world, it is obvious that there is a God.
Augustine of Hippo (AD 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.
Various forms of the argument from design have been used by Islamic theologians and philosophers from the time of the early Mutakallimun theologians in the 9th century, although it is rejected by fundamentalist or literalist schools, for whom the mention of God in the Koran should be sufficient evidence. While the argument from design was seen as an unconvincing sophism by the philosophers Al-Farabi and Avicenna, it was accepted by both the philosopher Averroes (Ibn Rushd) and his great anti-philosophy opponent Al-Ghazali. Averroes' term for the argument was Dalīl al-ˁināya, which can be translated as "argument from providence".
Averroes used teleological arguments in his interpretations of Aristotle from an Islamic perspective in Moorish Spain in the latter half of the 12th Century. His work was highly controversial, officially banned in both Christendom and Islamic Spain. Averroes' teleological arguments can be characterized as presuming one god. He proposes that order and continual motion in the world is caused by God's intellect. In knowing all forms and patterns, God provides order to the Lesser Intelligences.
Thomas Aquinas (1225-1274) presented a form of the teleological argument in his Summa Theologica. In his work, Aquinas presented five ways in which he attempted to prove the existence of God, the quinque viae. These arguments feature only a posteriori arguments, rather than literal reading of holy texts. He sums up his teleological argument as follows.
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. (St Thomas Aquinas—Summa Theologica: Article 3, Question 2)
Aquinas notes that the existence of final causes, by which a cause is directed toward an effect, can only be explained by an appeal to intelligence. However, as natural bodies aside from humans do not possess intelligence, there must, he reasons, exist a being that directs final causes at every moment. That being is what we call God.
The 17th-century Dutch writers Lessius and Grotius argued that the intricate structure of the world, like that of a house, was unlikely to have arisen by chance. The empiricist John Locke, writing in the late 17th century, developed the Aristotelian idea that, excluding geometry, all science must attain its knowledge a posteriori - through sensual experience. In response to Locke, Anglican Irish Bishop George Berkeley advanced a form of idealism in which things only continue to exist when they are perceived. When humans do not perceive objects, they continue to exist because God is perceiving them. Therefore, in order for objects to remain in existence, God must exist omnipresently.
David Hume, in the mid-18th century, presented arguments both for and against the teleological argument in his Dialogues Concerning Natural Religion. The character Cleanthes, summarizing the teleological argument, likens the universe to a man-made machine, and concludes by the principle of similar effects and similar causes that it must have a designing intelligence. Philo is not satisfied with the teleological argument, however. He attempts a number of refutations, including one that arguably foreshadows Darwin's theory, and makes the point that if God resembles a human designer, then assuming divine characteristics such as omnipotence and omniscience is not justified. He goes on to joke that far from being the perfect creation of a perfect designer, this universe may be "only the first rude essay of some infant deity... the object of derision to his superiors".
Look round the world: contemplate the whole and every part of it: You will find it to be nothing but one great-machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy, which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human design, thought, wisdom, and intelligence. Since therefore the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man; though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. By this argument a posteriori, and by this argument alone, do we prove at once the existence of a Deity, and his similarity to human mind and intelligence.
— David Hume, Dialogues Concerning Natural Religion
In 1713, William Derham published a book called Physico-Theology, which was "A demonstration of the being and attributes of God from his works of creation". A natural philosopher, he listed scientific observations of the many variations in nature, and proposed that these proved "the unreasonableness of infidelity". At the end of the section on Gravity for example, he writes:"What else can be concluded, but that all was made with manifest Design, and that all the whole Structure is the Work of some intelligent Being; some Artist, of Power and Skill equivalent to such a Work?" Also, of the "sense of sound" he writes:
For who but an intelligent Being, what less than an omnipotent and infinitely wise God could contrive, and make such a fine Body, such a Medium, so susceptible of every Impression, that the Sense of Hearing hath occasion for, to empower all Animals to express their Sense and Meaning to others.
He concludes: "For it is a Sign a Man is a wilful, perverse Atheist, that will impute so glorious a Work, as the Creation is, to any Thing, yea, a mere Nothing (as Chance is) rather than to God. 
A.S. Weber writes that this book "directly influenced" William Paley's later work.
The watchmaker analogy, framing the argument with reference to a timepiece, dates at least back to Cicero, who in his De Natura Deorum (II.88), reports a Stoic philosopher using such an argument against Epicureans, whom, he taunts, would "think more highly of the achievement of Archimedes in making a model of the revolutions of the firmament than of that of nature in creating them, although the perfection of the original shows a craftsmanship many times as great as does the counterfeit". It was also used by Robert Hooke and Voltaire, the latter of whom remarked:
The Universe troubles me, and much less can I think
That this clock exists and should have no clockmaker.
[S]uppose I found a watch upon the ground, and it should be inquired how the watch happened to be in that place, I should hardly think … that, for anything I knew, the watch might have always been there. Yet why should not this answer serve for the watch as well as for [a] stone [that happened to be lying on the ground]?… For this reason, and for no other; namely, that, if the different parts had been differently shaped from what they are, if a different size from what they are, or placed after any other manner, or in any order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it.
According to Alister McGrath, Paley argued that "The same complexity and utility evident in the design and functioning of a watch can also be discerned in the natural world. Each feature of a biological organism, like that of a watch, showed evidence of being designed in such a way as to adapt the organism to survival within its environment. Complexity and utility are observed; the conclusion that they were designed and constructed by God, Paley holds, is as natural as it is correct."
Natural theology strongly influenced British science, with the expectation as expressed by Adam Sedgwick in 1831 that truths revealed by science could not conflict with the moral truths of religion. These natural philosophers saw God as the first cause, and sought secondary causes to explain design in nature: the leading figure Sir John Herschel wrote in 1836 that by analogy with other intermediate causes "the origination of fresh species, could it ever come under our cognizance, would be found to be a natural in contradistinction to a miraculous process".
As a theology student, Charles Darwin found Paley's arguments compelling. However, he later developed his theory of evolution in his 1859 book On the Origin of Species, which offers an alternate explanation of biological order. In his autobiography, Darwin wrote that "The old argument of design in nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection has been discovered". Darwin struggled with the problem of evil of suffering in nature, but remained inclined to believe that nature depended upon "designed laws" and commended Asa Gray's statement about "Darwin's great service to Natural Science in bringing back to it Teleology: so that, instead of Morphology versus Teleology, we shall have Morphology wedded to Teleology."
Darwin owned he was "bewildered" on the subject, but was "inclined to look at everything as resulting from designed laws, with the details, whether good or bad, left to the working out of what we may call chance":
But I own that I cannot see, as plainly as others do, & as I shd wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice. Not believing this, I see no necessity in the belief that the eye was expressly designed. 
A modern variation of the teleological argument is built upon the concept of the fine-tuned Universe: According to the website Biologos: "Fine-tuning refers to the surprising precision of nature’s physical constants, and the beginning state of the Universe. To explain the present state of the universe, even the best scientific theories require that the physical constants of nature and the beginning state of the Universe have extremely precise values." Also, the fine-tuning of the Universe is the apparent delicate balance of conditions necessary for human life. In this view, speculation about a vast range of possible conditions in which life cannot exist is used to explore the probability of conditions in which life can and does exist.[note 1] In terms of a teleological argument, the intuition in relation to a fine-tuned universe would be that God must have been responsible, if achieving such perfect conditions is so improbable. However, in regard to fine-tuning, Kenneth Himma writes: "The mere fact that it is enormously improbable that an event occurred... by itself, gives us no reason to think that it occurred by design… As intuitively tempting as it may be...” Himma attributes the “Argument from Suspicious Improbabilities”, a formalization of “the fine-tuning intuition” to George N. Schlesinger:
To understand Schlesinger’s argument, consider your reaction to two different events. If John wins a 1-in-1,000,000,000 lottery game, you would not immediately be tempted to think that John (or someone acting on his behalf) cheated. If, however, John won three consecutive 1-in-1,000 lotteries, you would immediately be tempted to think that John (or someone acting on his behalf) cheated. Schlesinger believes that the intuitive reaction to these two scenarios is epistemically justified. The structure of the latter event is such that it… justifies a belief that intelligent design is the cause… Despite the fact that the probability of winning three consecutive 1-in-1,000 games is exactly the same as the probability of winning one 1-in-1,000,000,000 game, the former event… warrants an inference of intelligent design.
Himma considers Schlesinger’s argument to be subject to the same vulnerabilities he noted in other versions of the design argument:
While Schlesinger is undoubtedly correct in thinking that we are justified in suspecting design in the case [of winning] three consecutive lotteries, it is because—and only because—we know two related empirical facts about such events. First, we already know that there exist intelligent agents who have the right motivations and causal abilities to deliberately bring about such events. Second, we know from past experience with such events that they are usually explained by the deliberate agency of one or more of these agents. Without at least one of these two pieces of information, we are not obviously justified in seeing design in such cases… [T]he problem for the fine-tuning argument is that we lack both of the pieces that are needed to justify an inference of design. First, the very point of the argument is to establish the fact that there exists an intelligent agency that has the right causal abilities and motivations to bring the existence of a universe capable of sustaining life. Second, and more obviously, we do not have any past experience with the genesis of worlds and are hence not in a position to know whether the existence of fine-tuned universes are usually explained by the deliberate agency of some intelligent agency. Because we lack this essential background information, we are not justified in inferring that there exists an intelligent Deity who deliberately created a universe capable of sustaining life.
Antony Flew, who spent most of his life as an atheist, converted to deism late in life because of the anthropic principle. He concluded that the fine-tuning of the universe was too precise to be the result of chance, so accepted the existence of God. He said that his commitment to "go where the evidence leads" meant that he ended up accepting the existence of God. Flew proposed the view, held earlier by Fred Hoyle, that the universe is too young for life to have developed purely by chance and that, therefore, an intelligent being must exist which was involved in designing the conditions required for life to evolve.
Would you not say to yourself, “Some super-calculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule.” Of course you would… A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question.
— Fred Hoyle, Engineering and Science, The Universe: Past and Present Reflections
A version of the argument from design is central to both creation science and Intelligent design, but unlike Paley's openness to deistic design through God-given laws, they seek scientific confirmation of repeated miraculous interventions in the history of life, and argue that their theistic science should be taught in science classrooms.
The teaching of evolution was effectively barred from United States public school curricula by the outcome of the 1925 Scopes Trial, but in the 1960s the National Defense Education Act led to the Biological Sciences Curriculum Study reintroducing the teaching of evolution. In response, there was a resurgence of creationism, which was presented as "creation science", based on biblical literalism but with Bible quotes optional. ("Explicit references to the Bible were optional: Morris's 1974 book Scientific Creationism came in two versions, one with Bible quotes, and one without.")
A 1989 survey found that virtually all literature promoting creation science presented the design argument, with John D. Morris saying "any living thing gives such strong evidence for design by an intelligent designer that only a willful ignorance of the data (II Peter 3:5) could lead one to assign such intricacy to chance." Such publications introduced concepts central to intelligent design, including irreducible complexity (a variant of the watchmaker analogy) and specified complexity (closely resembling a fine-tuning argument). The United States Supreme Court ruling on Edwards v. Aguillard barred the teaching of "Creation Science" in public schools because it breached the separation of church and state, and a group of creationists rebranded Creation Science as "intelligent design" which was presented as a scientific theory rather than as a religious argument.
Scientists disagreed with the assertion that intelligent design is scientific, and its introduction into the science curriculum of a Pennsylvania school district led to the 2005 Kitzmiller v. Dover Area School District trial, which ruled that the "intelligent design" arguments are essentially religious in nature and not science. The court took evidence from theologian John F. Haught, and ruled that "ID is not a new scientific argument, but is rather an old religious argument for the existence of God. He traced this argument back to at least Thomas Aquinas in the 13th century, who framed the argument as a syllogism: Wherever complex design exists, there must have been a designer; nature is complex; therefore nature must have had an intelligent designer." "This argument for the existence of God was advanced early in the 19th century by Reverend Paley": "The only apparent difference between the argument made by Paley and the argument for ID, as expressed by defense expert witnesses Behe and Minnich, is that ID's 'official position' does not acknowledge that the designer is God."
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, established in Ancient Greece, in which science can not use supernatural explanations.
Intelligent design advocate Michael Behe proposed a development of Paley's watch analogy in which he argued in favour of intelligent design. Unlike Paley, Behe only attempts to prove the existence of an intelligent designer, rather than the God of classical theism. Behe uses the analogy of a mousetrap to propose irreducible complexity: he argues that if a mousetrap loses just one of its parts, it can no longer function as a mousetrap. He argues that irreducible complexity in an object guarantees the presence of intelligent design. Behe claims that there are instances of irreducible complexity in the natural world and that parts of the world must have been designed. This negative argument against step by step evolution ignores longstanding evidence that evolution proceeds through changes of function from preceding systems. The specific examples Behe proposes have been shown to have simpler homologues which could act as precursors with different functions. His arguments have been rebutted, both in general and in specific cases by numerous scientific papers. In response, Behe and others, "ironically, given the absence of any detail in their own explanation, complain that the proffered explanations lack sufficient detail to be empirically tested."
University of Chicago geneticist James A. Shapiro, writing in the Boston Review, states that advancements in microbiology etc., with its overlap with information science, have implications for the teleological argument. Shapiro states that these "natural genetic engineering" systems, such as genome reorganization can produce radical reorganizations of the "genetic apparatus within a single cell generation". Shapiro suggests what he calls a 'Third Way'; a non-creationist, non-Darwinian type of evolution:
What significance does an emerging interface between biology and information science hold for thinking about evolution? It opens up the possibility of addressing scientifically rather than ideologically the central issue so hotly contested by fundamentalists on both sides of the Creationist-Darwinist debate: Is there any guiding intelligence at work in the origin of species displaying exquisite adaptations ..."
In his book, Evolution: A View from the 21st Century, Shapiro refers to this concept of "natural genetic engineering", which he says, has proved troublesome, because many scientists feel that it supports the intelligent design argument. He suggests that "function-oriented capacities [can] be attributed to cells", even though this is "the kind of teleological thinking that scientists have been taught to avoid at all costs."
David Hume presented a criticism of the teleological argument in his Dialogues Concerning Natural Religion. The character Philo, a religious sceptic, voices Hume's criticisms of the argument. He argues that the design argument is built upon a faulty analogy as, unlike with man-made objects, we have not witnessed the design of a universe, so do not know whether the universe was the result of design. Moreover, the size of the universe makes the analogy problematic: although our experience of the universe is of order, there may be chaos in other parts of the universe. Philo argues:
A very small part of this great system, during a very short time, is very imperfectly discovered to us; and do we thence pronounce decisively concerning the origin of the whole?—David Hume, Dialogues 2
Philo also proposes that the order in nature may be due to nature alone. If nature contains a principle of order within it, the need for a designer is removed. Philo argues that even if the universe is indeed designed, it is unreasonable to justify the conclusion that the designer must be an omnipotent, omniscient, benevolent God - the God of classical theism. It is impossible, he argues, to infer the perfect nature of a creator from the nature of its creation. Philo argues that the designer may have been defective or otherwise imperfect, suggesting that the universe may have been a poor first attempt at design. Hume also pointed out that the argument does not necessarily lead to the existence of one God: “why may not several deities combine in contriving and framing the world?” (p. 108).
Wesley C. Salmon developed Hume's insights, arguing that all things in the universe which exhibit order are, to our knowledge, created by material, imperfect, finite beings or forces. He also argued that there are no known instances of an immaterial, perfect, infinite being creating anything. Using the probability calculus of Bayes Theorem, Salmon concludes that it is very improbable that the universe was created by the type of intelligent being theists argue for.
Nancy Cartwright accuses Salmon of begging the question. One piece of evidence he uses in his probabilistic argument - that atoms and molecules are not caused by design - is equivalent to the conclusion he draws, that the universe is probably not caused by design. The atoms and molecules are what the universe is made up of and whose origins are at issue. Therefore, they cannot be used as evidence against the theistic conclusion.
The teleological argument assumes that one can infer the existence of intelligent design merely by examination, and because life is reminiscent of something a human might design, it too must have been designed. However, considering "snowflakes and crystals of certain salts", "[i]n no case do we find intelligence". "There are other ways that order and design can come about" such as by "purely physical forces". 
The design claim can be challenged as an argument from analogy. Supporters of design suggest that natural objects and man-made objects have many similar properties, and man-made objects have a designer. Therefore, it is probable that natural objects must be designed as well. However, proponents must demonstrate that all the available evidence has been taken into account.
Most professional biologists support the modern evolutionary synthesis, not merely as 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. Over very long periods of time self-replicating structures arose and later formed DNA.
... from this sole argument I cannot conclude anything further than that it is probable that an intelligent and superior being has skillfully prepared and fashioned the matter. I cannot conclude from that alone that this being has made matter out of nothing and that he is infinite in every sense.
— Voltaire, Traité de métaphysique
Søren Kierkegaard questioned the existence of God, rejecting all rational arguments for God's existence (including the teleological argument) on the grounds that reason is inevitably accompanied by doubt. He proposed that the argument from design does not take into consideration future events which may serve to undermine the proof of God's existence: the argument would never finish proving God's existence. In the Philosophical Fragments, Kierkegaard writes:
The works of God are such that only God can perform them. Just so, but where then are the works of the God? The works from which I would deduce his existence are not directly and immediately given. The wisdom in nature, the goodness, the wisdom in the governance of the world -- are all these manifest, perhaps, upon the very face of things? Are we not here confronted with the most terrible temptations to doubt, and is it not impossible finally to dispose of all these doubts? But from such an order of things I will surely not attempt to prove God's existence; and even if I began I would never finish, and would in addition have to live constantly in suspense, lest something so terrible should suddenly happen that my bit of proof would be demolished.
— Søren Kierkegaard, Philosophical Fragments
Richard Dawkins is harshly critical of theology, creation and intelligent design in his book The God Delusion in which he contends that an appeal to intelligent design can provide no explanation for biology because it not only begs the question of the designer's own origin; but an intelligent designer must itself be far more complex and difficult to explain than anything it is capable of designing. He believes the chances of life arising on a planet like the Earth are many orders of magnitude less probable than most people would think, but the anthropic principle effectively counters skepticism with regard to improbability. For example, Fred Hoyle suggested that potential for life on Earth was no more probable than a Boeing 747 being assembled by a hurricane from the scrapyard. He argues that a one-time event is subject to improbability but once under way, natural selection itself is nothing like random chance. Furthermore, he refers to his counter argument to the argument from improbability by that same name:
The argument from improbability is the big one. In the traditional guise of the argument from design, it is easily today's most popular argument offered in favour of the existence of God and it is seen, by an amazingly large number of theists, as completely and utterly convincing. It is indeed a very strong and, I suspect, unanswerable argument—but in precisely the opposite direction from the theist's intention. The argument from improbability, properly deployed, comes close to proving that God does not exist. My name for the statistical demonstration that God almost certainly does not exist is the Ultimate Boeing 747 gambit.
The creationist misappropriation of the argument from improbability always takes the same general form, and it doesn't make any difference… [if called] 'intelligent design' (ID). Some observed phenomenon—often a living creature or one of its more complex organs, but it could be anything from a molecule up to the universe itself—is correctly extolled as statistically improbable. Sometimes the language of information theory is used: the Darwinian is challenged to explain the source all the information in living matter, in the technical sense of information content as a measure of improbability or 'surprise value'… However statistically improbable the entity you seek to explain by invoking a designer, the designer himself has got to be at least as improbable. God is the Ultimate Boeing 747.
…The whole argument turns on the familiar question 'Who made God?'… A designer God cannot be used to explain organized complexity because any God capable of designing anything would have to be complex enough to demand the same kind of explanation in his own right. God presents an infinite regress from which he cannot help us to escape. This argument… demonstrates that God, though not technically disprovable, is very very improbable indeed.
— Richard Dawkins, The God Delusion
Dawkins considered the argument from improbability to be "much more powerful" than the teleological argument, or argument from design, although he sometimes implies the terms are used interchangeably. He paraphrases St.Thomas' teleological argument as follows: “Things in the world, especially living things, look as though they have been designed. Nothing that we know looks designed unless it is designed. Therefore there must have been a designer, and we call him God.” 
George H. Smith, in his book Atheism: The Case Against God, points out what he considers to be a flaw in the argument from design:
Consider the idea that nature itself is the product of design. How could this be demonstrated? Nature… 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. (p. 268)
Richard Dawkins suggests that while biology can at first seem to be purposeful and ordered, upon closer inspection its true function becomes questionable. Dawkins rejects the claim that biology serves any designed function, claiming rather that biology only mimics such purpose. In his book The Blind Watchmaker, Dawkins states that animals are the most complex things in the known universe: “Biology is the study of complicated things that give the appearance of having been designed for a purpose.” He argues that natural selection should suffice as an explanation of biological complexity without recourse to divine provenance.
Proponents of intelligent design creationism, such as William A. Dembski question the philosophical assumptions made by critics with regard to what a designer would or would not do. Dembski claims that such arguments are not merely beyond the purview of science: often they are tacitly or overtly theological while failing to provide a serious analysis of the hypothetical objective's relative merit. Some critics, such as Stephen Jay Gould suggest that any purported 'cosmic' designer would only produce optimal designs, while there are numerous biological criticisms to demonstrate that such an ideal is manifestly untenable. Against these ideas, Dembski characterizes both Dawkins' and Gould's argument as a rhetorical straw man. He suggests a principle of constrained optimization more realistically describes the best any designer could hope to achieve:
Not knowing the objectives of the designer, Gould was in no position to say whether the designer proposed a faulty compromise among those objectives… In criticizing design, biologists tend to place a 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 to fall short of maximal function. 
— William A. Dembski, The Design Revolution: Answering the Toughest Questions About Intelligent Design