The logic of natural reasoning: formal or informal?

Background. The study is based on Piaget's theory of intellect development; Bryushinkin's logical-philosophical conception of logical procedure; logical theory of inferences. We regarde natural discourse as set of intellectual (including logical) procedures including constructing inferences. We assume that during the period of formal operations formation, the formal orientation of inferential procedures becomes dominant.

Objective. To reveal the cognitive grounds for differentiating of inferences in a holistic discursive context and constructing deductive reasoning.

Design. We elaborated special tests on: 1) selection of inferences in speech context; 2) inference macrostructure analysis; 3) selection of statements that allow the implementation of conclusion, 4) implementation of the inference procedure. The sample consists of middle and older adolescents and early youth respondents (on average, 100 respondents in each age group). The results of logical procedures implementation were qualitatively and quantitatively processed.

Results. The inferential activity of all respondents groups has some common features: 1) in holistic context, found “inferences” don't have logical features of inferences (without logical consequence relation); 2) functional differences between premises and conclusion are poorly differentiated; 3) meaningful and formal relations of statements-parcels act as cognitive bases for constructing inference, dominating type of relation depends on context; 4) violation of logical norms in inference is common; the success of solving problem depends on its features. The role of formal grounds for constructing inferences doesn’t increase.

Conclusion. The type of cognitive grounds of inference procedure isn’t stable - it depends on the type of inference and psychological "brightness" of its form or content features. Procedures aren’t formal (logical), but also aren’t informal (focused only on content of statements). Progressive development of procedures of constructing deductive reasoning isn’t natural. Logic education should be considered as the most important tool for transferring normative implementation of logical procedures from the zone of proximal to actual development one.