Venn diagrams were invented by a guy named John Venn (no kidding; that was really his name) as a way of picturing relationships between different groups of things. (Inventing this type of diagram was, apparently, pretty much all he ever accomplished. To add insult to injury, much of what we refer to as "Venn diagrams" are actually "Euler" diagrams. But we'll stick with the usual "Venn" terminology for the purposes of this lesson.) Since the mathematical term for "a group of things" is "a set", Venn diagrams can be used to illustrate both set relationships and logical relationships.