It's a characteristic of human thought that we divide the world into categories, and often into sequences or hierarchies where one level builds upon another, or is in some sense more abstract. Though these are human social constructions, these conceptual organizations do often derive from underlying physical Reality (see Modularity), so behaving in this way is adaptive. What are important kinds of levels?

Emergence is when complex unpredictable behavior arises from the interaction of simpler entities. Consider these levels of existence: subatomic particles → atoms → molecules → living cells → organisms → social groups. Every later (higher level) grouping is strictly dependent on the existence of all the lower levels, and for any change visible at a high level there must be some change in the arrangement or state of the components at each lower level. See Supervenience.

In our effort to understand the world, humans have developed methods and bodies of thought related to understanding particular emergent levels. Paralleling the above levels of existence, parts of physics concern themselves with the behavior of subatomic particles and atoms, while chemistry concerns itself with general properties governing the construction of molecules, cell biology studies the internal operations of cells, organisms in general are studied by biomechanics and evolutionary biology, with sub-specialties for particular species and organs (psychology, neuroscience), and behavior of social groups is studied in social psychology, sociology, Economics and ethology.

Abstraction and classification are powerful tools that we use to make sense of the world. The above analytic levels are an important special case of abstraction levels that we deliberately attach to the underlying physical reality of the corresponding emergent levels. Our Level Map of human reality shows some ways in which analytic levels may combine with more arbitrary classifications. This diagram does emphasize the emergence of mind from the physical world, but the layering also represents other kinds of relationships:

part-of:

The body is part of the world, and the brain and other organs are parts of the body.

representation:

The lowest levels, perception and Body Model represent the state of the world and of the body. Higher levels of unconscious processing (Emotion, etc.) represent the meaning of the situation relevant to the person's interest, while the highest level storytelling is a representation of the state of the unconscious mind (see The Interpreter Theory).

Pulling back to a higher conceptual level, we may go beyond developing abstract categories at a certain analytic level. We can instead propose new hierarchical organizations, with the understanding that multiple organizations and interpretations are useful, fluently switching between them as appropriate. This is precisely what we are doing here which this categorization of levels. When we adopt this sort of multi-level conceptual argument, some categories may be entirely unfamiliar, and take some getting used to before their value is appreciated. In Dennett's analysis of the intentional stance, the physical stance is well understood, but the design and intentional stances are more distinctive. See Intentional Design