 But there is one warning that survives from the old textbooks: If you formalise your argument in a way that is not a model-theoretic consequence, it doesn’t mean the argument is not valid. It may only mean that you failed to analyse the concepts in the argument deeply enough before you formalised. The old textbooks used to discuss this in a ragbag section called ‘topics’ (i.e. hints for finding arguments that you might have missed). Here is an example from Peter of Spain’s 13th century Summulae Logicales: