What are ordinal and cardinal numbers?
In common, arithmetic terms, cardinal numbersare those that express amounts; they
are also used in simple counting or to answer the question of quantity (how many).
They can be nouns (try counting to ten); as pronouns (tenwere discovered); or adjec-
tives (tencats). Specifically, the term is from the Latin cardin,meaning “stem” or
“hinge,” referring to the most important or principal numbers, with others depending
(hinging) on those numbers. We are most familiar with the cardinal numbers as our
counting numbers, or the Hindu-Arabic numeration system—1, 2, 3, and so on.
Ordinal numbersare much different. In common, arithmetic terms, ordinal num-
bers are adjectives that describe the numerical position of an object, such as first, sec-
ond, third, and so on. They are used to show the order of succession for objects (sec-
ondchair), names (secondmonth), or periods of time (2ndcentury).
Note that cardinal and ordinal numbers are easily divided. For example, in the
Hindu-Arabic numeration system, the cardinal numbers may be read as ordinals, such
as May 10 being read as “May tenth.” Such differences are even harder to distinguish
when it comes to Roman numerals. Most of the time, these numerals are considered
cardinal numbers (I, II, III, etc.), but they can also be ordinal numbers in certain con- 79
MATH BASICS
Anyone who has played a card game has used their knowledge of one-to-one correspondence, though most of us
would not know enough to call it that. The Image Bank/Getty Images.