Errors in deductive reasoning

The notion of rule concerning symbolic transformations bereft of any normative aspect is a common fundamental ingredient both of the presentation of any logical system and of the standard classical cognitive theory of the processing of mental representations. On the other hand, it is interesting to observe that merely speaking of misapplications or of non-applications of rules is not enough to account for reasoning errors from the cognitive point of view. To hint at what else is needed is the first main aim of this paper. Some notions, not all known from the literature, are introduced to build a quite comprehensive classification of the various kinds of errors underlying the data resulting from a longstanding intense experimental psychological activity. Finally, some open questions are raised concerning the concept of availability of a rule, the very general notion of competence in general and that of reasoning competence.