There are two kinds of numbers; ordinal and cardinal. Ordinal numbers denote rank or position in a system, while cardinal numbers tally how many units of something there are. You can think of ordinals ...
This is one of those quirky grammar rules that can be confounding because the rule for speaking differs from the rule for writing. Ordinal numbers show order, or a position in a series: first (1st), ...
Numbers can be used most flexibly to quantify, rank and identify. 'Cardinal' number refers to quantitative number assignments assessing set size (numerosity), whereas 'ordinal' number applies to ...