A previous critique of the relevance of Piron's questions-propositions system as a generator of quantum mechanics by interpretation is reinforced and brought to a close by further investigation.

In orthodox quantum mechanics, it has virtually become the custom to identify properties of a physical system with operationally testable propositions about the system. The causes and consequences of this practice are explored mathematically in this paper. Among other things, it is found that such an identification imposes severe constraints on the admissible states of the physical system.

A comprehensive formal system is developed that amalgamates the operational and the realistic approaches to quantum mechanics. In this formalism, for example, a sharp distinction is made between events, operational propositions, and the properties of physical systems.

A formal system of “questions” and “propositions” conceived by C. Piron and claimed to yield by interpretation quantum mechanics as well as all other known physical theories is examined. It is proved that the mentioned system is syntactically self-consistent in the sense of the theory of models. However, it is found that the mentioned formal system possesses certain syntactic characteristics in consequence of which qualification of this system as a generator of quantum mechanics by interpretation encounters semantic obstacles so grave (...) that they annihilate any relevance of such a qualification. (shrink)