Does formal logic make sense?
This text is a commentary on the book Logika i argumentacja. Praktyczny kurs krytycznego myślenia (Logic and Argumentation. A Practical Course In Critical Thinking) by Professor Andrzej Kisielewicz. Prof. Kisielewicz argues there, among other things, that formal (symbolic) logic is inadequate to explain practical rational reasoning. This commentary defends formal logic in this respect.
In particular, Prof. Kisielewicz proposes in his book a definition of (practical) logical inference. According to him, a conclusion follows from a given set of premises if there is no situation, where the premises hold, while the conclusion fails. In this commentary it is pointed out that this is a well-known notion of semantic inference in formal logic. It is also well-known that semantic and syntactic inference in logic are equivalent, i.e. equally strong.