Some interpretations of quantum mechanics regard a mixed quantum state as a ensemble, each individual member of which has a definite but unknown state vector. Other interpretations ascribe a state vector only to anensemble of similarly prepared systems, but not to anindividual. Previous attempts to detect the hypothetical individual state vectors have failed, essentially because the state operator enters the relevant equations linearly. An example from nonlinear dynamics, in which a density matrix enters nonlinearly, is examined because it might appear (...) to circumvent this difficulty. However, it is shown that the hypothetical individual state vectors can not be detected this way, so the adequacy of theensemble interpretation survives a critical test. (shrink)

The projection postulate, which prescribes “collapse of the state vector” upon measurement, is not an essential part of quantum mechanics. Rather it is only an optional discarding of certain branches of the state vector that are expected to be irrelevant for the purpose at hand. However, its use is hazardous, and there are examples of repeated measurements for which the conventional application of the projection postulate leads to incorrect results.

The attempt to derive (rather than assume) the statistical postulate of quantum theory from the many-universes interpretation of Everett and De Witt is analyzed The many-universes interpretation is found to be neither necessary nor sufficient for the task.

In their "traite de l'argumentation" perelman olbrechts indicate five factors contributing to the forces of arguments. the present paper is an analysis of each of these five factors taken in isolation; it indicates directions for operationalization of these factors. it stresses moreover that this multidimensional concept if it is to be used must lead to a weighted function of the five variables in order to be able to use the concept of "force of an argument." the absence of this weighted (...) function in po is deplored and it is argued that no theory of argumentation, even if it decides to remain completely descriptive, can be developed without definition of this weighted function. (shrink)