What is intelligent design?

William Dembski offers one definition:

Intelligent design is the study of patterns in nature that are best explained as the product of intelligence.

What is intelligence? Intelligence is teleological. It's basically about adapting means to ends. Intelligence is a causal power that can bring about purposes by arranging the means to bring those purposes about. An intelligence has to make choices. If it's adapting means, then it's this means, not that means. In fact, the very etymology of the word intelligence is inter lego - "to choose between". That's the characteristic of intelligence. Whereas something that operates by brute necessity always does the same sort of thing. Even chance is not really intelligence; it's not goal-directed. So it seems there's this fundamental distinction. Intelligence is about adapting means to ends.

The starting question for intelligent design is, what are the markers? How do we detect the effects of intelligence? There seem to be three main things we're looking for. Contingency: whether something happens that didn't have to happen. So it was optional. There are different live possibilities. Complexity: it was hard to reproduce by chance. If chance and necessity were operating, would it have been unlikely? And third specification: does it conform to some independently given pattern? So it's not just something we're imposing after the fact, that we're cherry-picking and looking for something that we're hoping is there, but that there's this independent pattern to which it conforms. If we have those three things that come into place, then it seems we're triangulated on the effects of intelligence.

So lots of questions are then open. What's the nature of that intelligence? What were the purposes of that intelligence? How did the intelligence implement that design?

Where intelligence design starts, not where it ends, is having reliable methods of design detection. Specifically: contingency, complexity, specification.

Also from Dembski (chapter 7, Design Revolution):

How does intelligent design differ from the design argument?

The design argument begins with features of the physical world that exhibit evidence of purpose. From such features, the design argument then attempts to establish the existence and attributes of an intelligent cause responsible for those features. Just which features signal an intelligent cause, what the nature of that intelligent cause is (e.g., personal agent or telic process) and how convincingly those features establish the existence of an intelligent cause remain subjects for debate and account for the variety of design arguments over the centuries. The design argument is also called the teleological argument.

Perhaps the best-known design argument is William Paley's. According to Paley, if one were to find a watch in a field, one could infer by observing the watch's adaptation of parts to telling time that it was designed by an intelligence. So too, according to Paley, the marvelous adaptations of means to ends in organisms ensure that organisms are the products of an intelligence. Paley published this design argument in his 1802 book (which carries a revealing subtitle), Natural Theology: Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature. Paley's project was to examine features of the natural world ("appearances of nature") and thereby draw conclusions about the existence and attributes of a designing intelligence responsible for those features (whom Paley identified with the God of Christianity).

Paley's business was natural theology. Intelligent design's business is much more modest: it seeks to identify signs of intelligence to generate scientific insights. Thus, instead of looking to signs of intelligence to obtain theological mileage, as Paley did, intelligent design treats signs of intelligence as strictly part of science. Indeed, within the theory of intelligent design, any appeal to a designer may be viewed as a fruitful device for un derstanding the world. Construed in this way, intelligent design attaches no significance to questions such as whether a theory of design is in some ultimate sense true, or whether the designer actually exists or what the attributes of that designer are.

Intelligent design is compatible with what philosophers of science call a constructive empiricist approach to scientific explanation. Constructive empiricism regards the theoretical entities of science pragmatically rather than realistically. Accordingly, the legitimacy of a scientific entity is tied not to its ultimate reality but to its utility in promoting scientific research and insight. On this view, theoretical entities are constructs with empirical consequences that are scientifically useful to the degree that they adequately account for a range of phenomena.

Scientists in the business of manufacturing theoretical entities like quarks, strings and cold dark matter could therefore view a designer as yet one more theoretical entity in their scientific tool chest. Ludwig Wittgenstein took such an approach. In Culture and Value he wrote, "What a Copernicus or a Darwin really achieved was not the discovery of a true theory but of a fertile new point of view." If intelligent design cannot be made into a fertile new point of view that inspires exciting new areas of scientific investigation, then (even if true) it will go nowhere. Yet before being dismissed, intelligent design deserves a fair chance to succeed.

The validity of the design argument, on the other hand, depends not on the fruitfulness of design-theoretic ideas for science but on the metaphysical and theological mileage one can get out of design. A natural theologian might point to nature and say, "Clearly, the designer of this ecosystem prized variety over neatness." A design theorist trying to do actual intelligent design research on that ecosystem might reply, "That's an intriguing theological assertion. Maybe I'll think about that after hours. Right now I'm looking into the sources of information for that variety."

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One final distinction about the design argument is helpful to keep in mind. Design arguments can focus on whether the universe as a whole is designed. Alternatively, they can focus on whether instances of design have occurred within an already given universe. The universe provides a well-defined causal backdrop. (Physicists these days think of it as a field characterized by field equations.) Although one can ask whether that causal backdrop is itself designed, one can ask as well whether events and objects occurring within that backdrop are designed. At issue here are two types of design: first, the design of the universe as a whole and, second, instances of design within the universe.

To illustrate the difference, consider the analogy of an oil painting. An oil painting is ordinarily painted on a canvas. One can therefore ask whether the canvas is designed. Alternatively, one can ask whether some configuration of paint on the canvas is designed. The design of the canvas corresponds to the design of the universe as a whole. The design of some configuration of paint corresponds to an instance of design within the universe.

In this analogy, the universe is a canvas on which is depicted natural history. One can ask whether that canvas is itself designed. On the other hand, one can ask whether features of natural history depicted on that canvas are designed. In biology, for instance, one can ask whether an irreducibly complex biochemical machine like the bacterial flagellum is designed. Although design remains a much discussed topic in cosmology (is the universe as a whole designed?), with intelligent design's focus on biology, most of the discussion and controversy now centers on biology (is there design in the universe and, specifically, in biology?).