Why do ten and twenty get unique words?

Question

onety, twety (two-ty), thirty, fourty, fifty, sixty...

Most of the count is consistently named using 0 through 9 with hundred (ten tens), thousand (hundred tens), etc. -- there are only four exceptions.

I am teaching my son counting. He is confused by the breaks in the pattern for ten (wiki has no explanation for origin) and twenty (two tens per wiki; does not help since twoty also would mean two tens).

Why ten at all, shouldn't it be zero, one-zero, two-zero, three-zero... (that thought runs out at nine-zero). Forgetting repeating zero and instead sticking with named order of magnitudes:

• ... Zero
• One zero, Two zero, Three zero, Four zero... Ten (Ty)

• One ten, Two ten, Three ten, Four ten... Hundred

  • Onety-one, Onety-two, Onety-three, Onety-four... Twoty
  • Twoty-one, Twoty-two, Twoty-three, Twoty-four... Threety
  • Threety-one, Threety-two, Threety-three, Threety-four... Fourty
  • Fourty-one, Fourty-two, Fourty-three, Fourty-four... Fivety

• One hundred, Two hundred, Three hundred... Thousand

• One thousand, Two thousand, Three thousand... Million

This article goes into more detail on these inconsistencies: "Linguistic influence on mathematical development is specific rather than pervasive: revisiting the Chinese Number Advantage in Chinese and English children" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4341514/

There is a similar question about eleven and twelve as opposed to oneteen and twoteen: Why do eleven and twelve get unique words and not end in "-teen"? They explain the orgin of the words as old german with reference to the position relative to ten; essentially 'first over from ten' and 'second over from ten.' My son was also confused by these but the link above answered this.

A question for the mixed use of 'thir' instead of 'three' in thirteen but four for fourteen: Why is it "thirteen" and not "threeteen"?

A close issue is the shifts in format from order-of-magnitude name + count: Why is there a "one" before "hundred", "thousand", etc. but not "ten"? Which has at times been more consistent: 19th century English texts occasionally use Germanic-style number words, such as "four-and-twenty". When did this fall out of use?

EDIT: I modified the question (removed firsty and seconty) to reflect a better understanding between ordinal and cardinal and misassociation of thirty and fifty to ordinal origins, thank you @rjpond

Answer 1

why isn't ten one-ty?

In general

The numbers are among the oldest words in the language. They haven't been designed by a committee to be logical and consistent. But there is often more logic there than it might appear at a glance.

Ten

The ty suffix means ten, so one-ty would mean one ten. Why not just have a word for ten? The -teen suffix likewise references "ten".

Twenty

The "w" of "two" would originally have been sounded, making "twenty" more consistent. In Old English, "two" had the "w" in its masculine and feminine forms but not in its neuter form. The "w" survives in German (albeit pronounced as a "v").

The reason for the "n" in "twenty" (and in its German and Dutch cognates) is uncertain: "the first element [of the word 'twenty'] is variously explained as a nominative plural (Old English twégen) and as a dative form" (OED). This "n" is absent from the Norse equivalent.

Eleven and Twelve

The word "eleven" is of uncertain origin, although in Old English it was "endleofen", of which the "en" means "one". Other Germanic languages have similar words (German "elf") and the word goes all the way back to early Germanic.

"Twelve" is based on the word "two". Again it has cognates in the other Germanic languages.

One theory is that "eleven" and "twelve" originally meant "one left" and "two left" after reaching ten. (See "twelve" in the OED.)

Ordinals

"Thirty" etc are derived from the cardinal forms "three" etc (or rather from their distant ancestors) rather than from ordinals. The Old English form of "thirty" was "thritig". Though a process called metathesis the "r" and an adjacent vowel get swapped round. And the same thing happened in the word "third" (OE "thridda"). This doesn't mean that "thirty" or "fifty" come from the ordinals.

Zero

The concept of zero didn't really reach the West until the 12th century. Western Arabic numerals (0, 1, 2, 3...) were barely known in the West until the 10th century and even then not much used until the 15th century. There was no widely accepted Roman numeral for zero. The English language and its system of counting (excluding the word "zero", which is only a few hundred years old in English) are many centuries older than the Western adoption of these numerals or of the concept of zero as a number.

Hundred, thousand, million

"Million" and bigger numbers are relatively recent borrowings from French (1500s and later). "Hundred" and "thousand" go back to Old English and beyond, though. Originally in the pre-Old English period, "thousand" probably just meant "multitude" (such large numbers rarely being needed). "Hundred" has usually meant a hundred in English, but it is unclear whether it originally meant a hundred or 120: the OED etymology implies that the latter might be "an older usage". Forms equivalent to "tenty" or "ten tens" were used in Old High German, Gothic and Old Norse, but today all the Germanic languages use "hundred" or a close cognate term.