Configurations of the trilateral diagram meaningful in this context are collected in a special table . Remark Much as Venn diagrams , trilateral diagrams rely on our geometric intuition. When you place a red counter on the diagram you mean to make an assertion of existence. When you say Some m are x the intention is usually to Some m exist , Some x exist , and, in addition, Some m are x . Strangely, this view point may not be logically viable.
All green pigs are green .
Therefore, Some x are y meaning that green pigs exist which may no be true. Formalism of Boolean Algebra easily detects this pitfall. Alexander Bogomolny 2789881 .