Among the most pressing challenges for dream science is the difficulty of establishing

theoretical unification between the various theories, ideas, and findings

that have been presented in the literature to answer the question of how it is possible

to construct a solid scientific theory with predictive and explanatory power

in dream science. We suggest that the concept of “world-simulation” serves as the

core concept for a theoretically unified paradigm to describe and explain dreaming.

From this general concept, more specific theories of the function of dreaming

can be derived, such as the Threat Simulation Theory (TST) and the Social Simulation

Theory (SST), as we argued in our target article. We agree with Dresler

that these two functions may not be the only functions of dreaming, but we still

have grounds to believe that they are the strongest contenders. In our reply we

first clarify why the functions of sleep should be considered separately from the

functions of dreaming. Second, we outline what a good scientific theory of dreaming

should be like and what it should be capable of. Furthermore, we evaluate the

current state of simulation theories within this context. To conclude, we propose

that instead of a general multifunctional theory of sleep and dreaming, where no

hypothesis is excluded, the future progress of dream science will benefit more from

opposing, competing and mutually exclusive theories about the specific functions

of dreaming. This, however, demands that the opposing theories and their predictions

must be risky, clearly formulated, and empirically testable.