By the end of the modern period, a particular world view had become firmly entrenched in the public understanding. Unlike most philosophical positions, which are sharply distinguished from scientific theories, this world view was widely seen as a direct implication of science, and even as the sine qua non for all scientific activity. For shorthand, let's call this view “materialism.”

Materialism consisted of five central theses:

1. Matter is the fundamental constituent of the natural world.

2. Forces act on matter.

3. The fundamental material particles or “atoms” – together with the fundamental physical forces, whatever they turn out to be – determine the motion of all objects in nature. Thus materialism entails determinism.

4. All more complex objects that we encounter in the natural world are aggregates of these fundamental particles, and their motions and behaviors can ultimately be understood in terms of the fundamental physical forces acting on them. Nothing exists that is not the product of these same particles and forces. In particular, there are no uniquely biological forces (vitalism or “entelechies”), no conscious forces (dualism), and no divine forces (what came to be known as supernaturalism). Thus materialism implied the exclusion of dualism, downward causation (Bøgh Andersen et al., 2000), and divine activity.

5. Materialism is an ontological position, as it specifies what kinds of things do and do not exist. But it can also become a thesis concerning what may and may not count as a scientific explanation. When combined with a commitment to scientific reduction, for example, it entails that all scientific explanations should ultimately be reducible to the explanations of fundamental physics. Any other science, say biology or psychology, is incomplete until we uncover the laws that link its phenomena with physics. In its reductionist form – which historically has been its most typical form – materialism thus excludes interpretations of science that allow for “top-down” causation, also known as “strong emergence.” Materialists may be divided on whether, and if so how soon, these reductions will actually be accomplished. Still, it is an entailment of materialism in most of its modern forms that an omniscient knower would be able to reduce all higher-order phenomena to the locations and momentums of fundamental particles.