Reductive theories of neuroscience generally rely on the assumption that the mechanisms accounted for at lower levels of description account for the phenomena seen at higher levels. Thus, biochemistry is explained as due to atomic and chemical mechanisms, cell biology explained via biochemical mechanisms, and brain neurophysiology explained as an outcome of cellular physiological mechanisms.
What is "mechanism" in these theories? Mechanism is an explanation of a thing in terms of "objective" properties instead of its "subjective" qualities. Such a distinction is one considered by many to be the properly "scientific" one since the physics of the time of Galileo. Says Wikipedia:
The primary/secondary quality distinction is a conceptual distinction in epistemology and metaphysics, concerning the nature of reality. It is most explicitly articulated by John Locke in his Essay concerning Human Understanding, but earlier thinkers such as Galileo and Descartes made similar distinctions.
Primary qualities are thought to be properties of objects that are independent of any observer, such as solidity, extension, motion, number and figure. These characteristics convey facts. They exist in the thing itself, can be determined with certainty, and do not rely on subjective judgments. For example, if a ball is round, no one can reasonably argue that it is a triangle.
Secondary qualities are thought to be properties that produce sensations in observers, such as color, taste, smell, and sound. They can be described as the effect things have on certain people. Knowledge that comes from secondary qualities does not provide objective facts about things.
Primary qualities are measurable aspects of physical reality. Secondary qualities are subjective.
"Extension, motion, number, and figure," along with emergent but related qualities such as temperature, are used to configure the lower level things to account for the properties of higher levels. For example, the configuration of the neuron in cell biology terms is used to account for the neural circuitry of the reflex response in neuroscience: the cells are extended (in the Lockean sense of filling a particular area or volume) and numbered so as to make up the reflex arc in their function. Thus, reduction: we have used basic, objective properties of the lower level objects to create new objects with new properties, but all is explainable by "basic" physics.
The problem then is that we have not truly used anything that current physics considers physically basic in our reduction!
Currently, particle physics considers a few properties such charge, spin, momentum, and mass to be fundamental, and suggests that all other physical properties are emergent from those base intrinsic properties. By those measures, the "primary" qualities are in reality secondary ones. Perhaps Galileo's secondary qualities are then tertiary ones?
What is clear is that the eliminativist or illusionist about aspects of human experience will always go for elimination of something such as the "illusion" of time or the self, and will neglect attempting the elimination of other human experiences, such as distance or location. Why? For those too are emergent, relative, non-basic properties, or so quantum mechanics tells us!
It is an outmoded, obsolete mechanistic view of the universe that directs the eliminativist to what he seeks to reduce and then call illusion. Garbage in, garbage out.
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