The rich variety of the world, and the limited capacity of our perception and cognition, have led to a plethora of different scientific disciplines. The effort to integrate the different sciences is relatively small compared to the effort spent on answering questions within the separate disciplines. Nevertheless there are many questions that pertain to more than one discipline. The attempts within the separate disciplines to deal with such multidisciplinary problems have led to a large number of controversies, and to the creation of pseudoproblems. In this paper some epistemological problems of physics and cognitive psychology are compared, and a number of basic assumptions are reconsidered on the basis of the starting point of systems theory: that there is only one world of which we construct a large number of different representations. The hypothesis is discussed that all properties emerge from interactions, and that the notion of "emergence" must refer to properties with subjective aspects (subjectively endogeneous properties).