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The term scientific reductionism has been used to describe various reductionist ideas about science. ^[1] These ideas can often be conflicting.

One version is simply the idea that all of nature can eventually be described scientifically; that there are no inherently unknowable facts.

Sometimes it is used to describe science (particularly physics) as a basis for ontological reductionism—the idea that everything that exists can be explained as the interactions of a small number of simple things (such as fundamental particles like quarks and leptons interacting through gauge bosons) obeying physical laws. Superstitious world-views have however been largely abandoned in the scientific community in exchange for more naturalistic approaches with empirical evidence to support them.

One attack against this form of reductionism argues that it is incorrect to regard the laws which govern the components of structures to be more fundamental than the laws which govern the structures. For example, a traffic jam may contain patterns of behavior which cannot be reduced to the behavior of an individual car. Similarly metals undergo collective behavior and interactions that are not reducible to the behavior of an individual atom within that metal. It is argued that the principles which describe this collective behavior are no less fundamental than the laws that describe the atoms themselves.

Daniel Dennett defends this basic kind of reductionism, which he says is really little more than materialism, by making a distinction between this and what he calls "Greedy reductionism": the idea that every explanation in every field of science should be reduced all the way down to particle physics or string theory. Greedy reductionism, he says, deserves some of the criticism that has been heaped on reductionism in general because the lowest-level explanation of a phenomenon, even if it exists, is not always the best way to understand or explain it. Richard Dawkins describes the alternative as "hierarchical" reductionism^[2]: organisms can be described in terms of DNA, DNA in terms of atoms, atoms in terms of sub-atomic particles; but there is no need to deal with details of sub-atomic particles to explain animal behavior if one can make adequate explanations and predictions at a higher level.

Both Dennett and Steven Pinker argue that too many people who are opposed to science use the words "reductionism" and "reductionist" less to make coherent claims about science than to convey a general distaste for the endeavor. Furthermore, these opponents often use the words in a rather slippery way, to refer to whatever they dislike most about science. Dennett suggests that critics of reductionism may be searching for a way of salvaging some sense of a higher purpose to life, in the form of some kind of non-material / supernatural intervention. Dennett terms such aspirations "skyhooks," in contrast to the "cranes" that reductionism uses to build its understanding of the universe from solid ground. He writes :-

The term that is most often bandied about in these conflicts, typically as a term of abuse, is "reductionism." Those who yearn for skyhooks call those who eagerly settle for cranes "reductionists," and they can often make reductionism seem philistine and heartless. But like most terms of abuse, "reductionism" has no fixed meaning. (Dennett 1995, p. 80)

As Pinker puts it,

Attempts to explain behavior in mechanistic terms are commonly denounced as "reductionist" or "determinist." The denouncers rarely know exactly what they mean by those words, but everyone knows they refer to something bad. (Pinker 2002, p. 10)

In recent years, the development of systems thinking has provided methods for tackling issues in a holistic rather than a reductionist way, and many scientists approach their work in a holistic paradigm. When the terms are used in a scientific context, holism and reductionism refer primarily to what sorts of models or theories offer valid explanations of the natural world; the scientific method of falsifying hypotheses, checking empirical data against theory, is largely unchanged, but the approach guides which theories are considered. The conflict between reductionism and holism in science is not universal--it usually centers on whether or not a holistic or reductionist approach is appropriate in the context of studying a specific system or phenomenon.

In many cases (such as the kinetic theory of gases), given a good understanding of the components of the system, one can predict all the important properties of the system as a whole. In other cases, trying to do this leads to a fallacy of composition. In those systems, emergent properties of the system are almost impossible to predict from knowledge of the parts of the system. Complexity theory studies such systems.

• Daniel Dennett (1995) Darwin's Dangerous Idea: Evolution and the Meanings of Life. ISBN 0-684-80290-2
• Steven Pinker (2002) The Blank Slate: The Modern Denial of Human Nature. Viking Penguin.
• Steven Weinberg (2002) describes what he terms the culture war among physicists in his review of A New Kind of Science
• Eric Scerri The reduction of chemistry to physics has become a central aspect of the philosophy of chemistry. See several articles by this author.