Numerals
Cardinal and ordinal numbers, their spelling and the suffixes that form them.
Numerals are words that show quantity (cardinal numbers: one, two, three) or order/position (ordinal numbers: first, second, third). Most cardinal numbers from 13 to 19 end in the suffix -teen (thirteen, fourteen, fifteen), while the tens from 20 to 90 end in the suffix -ty (twenty, thirty, forty). Watch the spelling changes: 'four' keeps its -u in 'fourteen' but 'forty' drops it; 'five' becomes 'fifteen' and 'fifty'; 'eight' becomes 'eighteen' and 'eighty' (only one extra t); 'nine' becomes 'nineteen' but 'ninety' drops the final e. Most ordinal numbers are formed by adding the suffix -th to the cardinal number (four -> fourth, six -> sixth, ten -> tenth), but the first three are irregular: one -> first, two -> second, three -> third. Ordinals ending in -y change to -ieth (twenty -> twentieth, thirty -> thirtieth). Numbers combining tens and units use a hyphen (twenty-one, forty-fifth), and in compound ordinals only the last part becomes ordinal (twenty-first, ninety-ninth). Cardinal numbers are used for years and quantities, while ordinal numbers are used for dates written in full (the first of May) and for rank or sequence (my third try, the fifth floor).
Key terms
| Cardinal | Ordinal | Note |
|---|---|---|
| one | first | irregular |
| two | second | irregular |
| three | third | irregular |
| five | fifth | drops final -e |
| eight | eighth | drops second -t |
| nine | ninth | drops final -e |
| twelve | twelfth | -ve -> -f + th |
| twenty | twentieth | -y -> -ieth |
| Number | -teen form | -ty form |
|---|---|---|
| 4 | fourteen | forty (no u) |
| 5 | fifteen (irregular base) | fifty (irregular base) |
| 8 | eighteen (one extra t) | eighty (one extra t) |
| 9 | nineteen | ninety (drops -e) |
- 1Start: The cardinal number is 'nine'.
- 2Apply the rule: Most ordinals add -th, but a final silent -e is dropped first.
- 3Answer: nine -> ninth (not nineth).
- 1Start: We need the ordinal of 'ninety-nine'.
- 2Apply the rule: Only the last word of a compound number becomes ordinal; 'ninety' stays cardinal and 'nine' becomes 'ninth'.
- 3Answer: ninety-nine -> ninety-ninth.
Do not write 'fourty' - the tens form of 'four' drops the 'u': the correct spelling is 'forty'.
The ordinals of one, two and three are irregular: 'first', 'second', 'third', not 'oneth', 'twoth' or 'threeth'.
Numbers ending in -y change to -ieth for the ordinal: 'twentieth', 'thirtieth', not 'twentyth' or 'thirtyth'.
In a compound number only the final part becomes ordinal: 'twenty-first', 'thirty-second', 'forty-third' - the first part stays in its cardinal form.
Rules
- 1Cardinal numbers 13-19 end in -teen (thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen); watch spelling: fifteen, eighteen (one extra t), nineteen.
- 2Cardinal tens 20-90 end in -ty (twenty, thirty, forty, fifty, sixty, seventy, eighty, ninety); forty drops the 'u' of four, and ninety drops the final 'e' of nine.
- 3Most ordinal numbers add -th to the cardinal (four -> fourth, six -> sixth, ten -> tenth, twelve -> twelfth); the first three are irregular: one -> first, two -> second, three -> third.
- 4Ordinals ending in -y change y to -ieth: twenty -> twentieth, thirty -> thirtieth, forty -> fortieth, ninety -> ninetieth.
- 5Compound numbers use a hyphen, and only the last word of a compound ordinal takes the ordinal form: twenty-one -> twenty-first, ninety-nine -> ninety-ninth.
Practice
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