The numerals and derived numbers of the Proto-Indo-European language (PIE) have been reconstructed by modern linguists based on similarities found across all Indo-European languages. The following article lists and discusses their hypothesized forms.
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Cardinal numbers
The cardinal numbers are reconstructed as follows:
Other reconstructions typically differ only slightly from Beekes and Sihler. A nineteenth century reconstruction (by Brugmann) for thousand is *tūsḱmtiə. See also Fortson 2004.
The elements *-dḱomt- (in the numerals "twenty" to "ninety") and *dḱm̥t- (in "hundred") are reconstructed on the assumption that these numerals are derivatives of *deḱm̥(t) "ten".
Lehmann believes that the numbers greater than ten were constructed separately in the dialects groups and that *ḱm̥tóm originally meant "a large number" rather than specifically "one hundred."
Gender of numerals
The numbers three and four had feminine forms with the suffix *-s(o)r-, reconstructed as *t(r)i-sr- and *kʷetwr̥-sr-, respectively.
Numerals as prefixes
Special forms of the numerals were used as prefixes, usually to form bahuvrihis (like five-fingered in English):
Ordinal numbers
The ordinal numbers are difficult to reconstruct due to their variety in the daughter languages. The following reconstructions are tentative:
The cardinals ending in a syllabic nasal (seven, nine, ten) inserted a second nasal before the thematic vowel, resulting in the suffixes *-mó- and *-nó-. These and the suffix *-t(ó)- spread to neighbouring ordinals, seen for example in Vedic aṣṭamá- "eighth" and Lithuanian deviñtas "ninth".
Reflexes
Reflexes, or descendants of the PIE reconstructed forms in its daughter languages, include the following.
Reflexes of the cardinal numbers
In the following languages, reflexes separated by slashes mean: