# What Is the Difference Between a Function and a Relation?

**A relation is a set of numbers that have a relationship through the use of a domain and a range, while a function is a relation that has a specific set of numbers that causes there to be only be one range of numbers for each domain of numbers.** All functions are relations, but all relations are not functions.

There are numbers that are related to each other in every relation. There could be a large variety of numbers in the domain for a given range. For example, if x is equal to 23, then y could be equal to 46 or 11.5, depending on the factors that are being played into the domain.

In a function, the numbers will always be able to relate back to a single number out of the range of numbers. It can be concluded that if x equals 13, then y will always equal 26. There may be many numbers in a domain that lead to the same range in a function, but there will never be more numbers in a range than a domain. If the number of x changes to 14, then y will change to 28. Many mathematicians use the term "well behaved" for numbers that are part of a function.