# Cardinality

An infinite set is considered countable if they can be listed without missing any. Examples include the rational numbers, integers, and natural numbers. Such sets have a cardinality that we call $\aleph_0$ (read as: aleph null, aleph naught or aleph zero). Sets such as the real numbers are not countable. If given any finite or infinite list of real numbers, you can create a number not on that list. The real numbers have a cardinality of c.