does a venn diagram always use 2 or 3 circles 
while often employing a pair or triplet of circles venn diagram can use any number of circles or any other shape to show the differences and intersections of different sets the bottom linevenn diagrams are an efficient way to express the relationship between items and which attributes they have in common since they help visualize the similarities and differences between limited sets of things they are widely used in education probability logic statistics linguistics and computer science 