In this paper, we present a novel approach to identify fallacies through formal constraints, as a viable alternative to more traditional fallacy classifications by informal criteria. To achieve this objective, we introduce a novel argumentation model, the theme aspect argumentation model, which can do both: modelling of a given argumentation as it is expressed (rhetoric modelling); and deeper semantic analysis of the rhetoric argumentation model. By the help of formal constraints on the theme aspect argumentation model, it is for example possible to see if 'attack's which are claimed to be attacks at the rhetoric level are really attacks. We present core formal constraints that a reasonable argumentation should observe, and then more formal constraints that improve fallacy identification capability. We show and prove consequences of these formal constraints. We then define the concept of normal forms and that of logico-rhetorical conclusion, which we use to demonstrate detection of specific fallacies, informal and logical.