ABSTRACT
Venn diagrams are named after John Venn, but he’s definitely not their creator. When placing numbers in sections of a Venn diagram, it should surprise no one that if there are more numbers than sections, one number must be left over or one section would have to have two numbers placed in it, which would not be appropriate. What may be surprising is that this is considered a mathematical principle and is important enough to have a name attached to it. Euler diagrams also came before Venn diagrams. However, they were different in an important way. Areas of intersection are only shown in Euler diagrams if the intersection is nonempty, while for Venn diagrams intersections and other sections can be empty. Insisting that the diagrams consist only of circles would be a mistake, because if we wish to consider all possible intersections of four sets, a diagram is not even possible with circles alone.
