2.10 THE IDEA OF DIAGRAMS

The universally known Venn diagrams (actually Euler's) also trace their historical lineage up to Llull. He was the first to represent graphically his "concepts" by circles and link them by superposing and intersecting them (though his aim was not to show whether they had an intersection but to demonstrate that they had a more or less strong affinity). (He also linked the terms of a syllogism with a triangle, in what was later called "pons asinorum".) Llull's circle drawings of concepts became a learning aid in J. L. Vives' hands in the l6th century, and were perfected in the l7th by Sturm or Leibniz -who created a whole (unpublished) logical notation out of them- and finally, yes, Euler (in the 1760's). (Now we call them, improperly, Venn's diagrams.)