Using logical conjunctions in everyday language in a way different from that used in the language of science represents a serious obstacle. An alternative in common language is always understood as exclusive. Differentiating between implication and identity depends on the context, even when conjunctions are used, such as "if, then", not to mention "since" or "because". Causality is mistaken for logical dependence and vice versa. Using logical rules separately from context in a formal, conscious way requires - as demonstrated by Piaget - fully developed formal thinking, which may not be attained by everybody. It seems, in fact, that the majority of society never reaches this stage. They apply logically correct reasoning in familiar situations only. Ten years ago I conducted standard tests with groups of 11-year-olds, 15-year-olds (university-linked class), and adults. A surprisingly large number of the 11-year-olds (ca 40%, i.e. comparable with the adults' results) could manage problem solving quite well. High school students had the best results. All errors in students answers stemmed from the fact of their not being able to leave the context framework and to apply formal (for all groups) rules of logic.