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(in 1614). The first detailed elaboration of these diagrams can be traced back to Erhard Weigel (1625-1699), who called this type of diagram a 'logometrum' (a measuring instrument for logic). Weigel was the first to prove all valid syllogisms with the aid of shapes in a two-dimensional plane. In the case of generally affirmative judgements (all-sentences), the geometric shape for the subject should lie completely within the shape for the predicate. In the case of negative judgements (no-sentences), it should

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