It's the same temperature, as measured by the thermometer, but one person experiences miserable cold, while another experiences a refreshing chill. Which experience is 'true' or 'real.' Or are both experiences illusions (i.e., purely subjective)?
Most introductory psychology texts describe an experiment in which the participant leaves one hand in a bucket of ice water and another hand in a bucket of hot water for a few minutes, then simultaneously puts both hands into a bucket of water at room temperature. What happens? One hand experiences the water as being warm, while the other hand experiences the bucket as being cold.
Does this demonstrate that perception is illusionary? Or does it suggest that the experience of temperature is dynamic. That it reflects change, or relations over time (as opposed to isolated events in time).
Imagine two intersecting lines on a graph one sloping down and the other sloping up. At the intersection, both point values are identical - but the slopes are different. Classically, we have tended to treat human experience as if it were a collection of isolated points in time. Thus, we have failed to consider that the slopes may be different.
If experience is dynamic, then it is essential that we consider the points as integrated components of the line. Rather than isolating behavior in time, we need to examine behavior over time (we need to consider the lines).
From the perspective of dynamics, the experiences of both people can be real. Both experiences are partial functions of the current physical temperature (as measured by a thermometer), but they are also functions of different past histories and different potential futures (e.g., intentions). Though the temperature 'points' may be the same for both, the slopes may be very different. The experiences may be situated on different trajectories.
When the different experiences are dismissed as 'subjective,' there is an implication that all experience is illusionary. That experiences are groundless with respect to the objective physical situations (e.g., the objective temperature). That experiences are 'in the head.' However, if you view experience as a dynamic property over time (e.g., with both a position and a velocity or slope), then you can see that the differences may be due to the fact that both are grounded, but in different ways. In this context, both experiences can be considered to be 'real' (in the sense that they are grounded, but with respect to objectively different situations).
Note that (as with constructs such as affordance) the 'situation' is not purely physical (objective) or purely mental (subjective). Both the situation and the experience are dynamical phenomenon reflecting both where agents are coming from and where agents are going. And that trajectory is shaped by both objective physical properties (e.g., the temperature) and by mental properties (e.g., an intention).
Cognitive Science will resolve many mysteries and contradictions, if it will only connect the dots and begin to consider trajectories as the fundamental units of analysis.