Six
The PIE Root
Few words in any language carry the weight of evidence that low numerals do. *\*Swéḱs* is reconstructed with high confidence precisely because it survives intact, with predictable sound changes, across every major branch of the Indo-European family. Numerals are among the least borrowed items in any vocabulary — a language does not import the word for 'six' from a trading partner. When the same root appears in Sanskrit and Welsh, in Lithuanian and Armenian, the explanation is common ancestry.
The Cognate Chain
The reflex of *\*swéḱs* in every branch tells a consistent story:
- Sanskrit *ṣáṣ* - Greek *héx* (ἕξ) - Latin *sex* - Gothic *saihs* - Old English *siex*, *six* - Old High German *sehs*, Modern German *sechs* - Lithuanian *šeši* - Old Church Slavonic *šestĭ*, Russian *šestʹ* (шесть) - Welsh *chwech* - Armenian *vec'* (վեց) - Albanian *gjashtë* - Tocharian A *ṣäk*, Tocharian B *ṣkas*
The spread is total. Every branch that has been studied preserves a recognisable reflex of the same ancestral form.
Grimm's Law in Action
The correspondences between Latin and Germanic are not accidental resemblances — they are the output of a sound law. Jakob Grimm formulated the shift that separates Proto-Germanic from the rest of the family. The voiceless stops of PIE underwent a systematic change: *\*p → f*, *\*t → þ*, *\*k → h/x*.
Latin *sex* and Old English *siex* are the same word. The medial consonant in Latin is /k/ (written ⟨x⟩ as a digraph for /ks/); in Germanic, that same PIE velar has shifted to /x/, audible in the modern German *sechs* and preserved in the Old English spelling *siex*. Latin *sex* : Old English *siex* is a textbook demonstration of the First Germanic Sound Shift. Once you see it, the family resemblance is not merely visible — it is mechanically predicted.
Three English Forms from One Root
English has inherited *\*swéḱs* three times over, through three different channels:
1. The Germanic form: *six*. The everyday English word, inherited directly through Proto-Germanic *\*sehs* and Old English *siex*.
2. The Greek form: *hexa-*. Greek *héx* enters English through learned and scientific vocabulary — *hexagon* (six-angled), *hexameter* (six-measure verse), *hexadecimal* (base sixteen, named for the six that begins the prefix). This channel opened through Latin transmission of Greek texts, then accelerated with Renaissance scholarship.
3. The Latin form: *sex-* / *sext-*. Latin *sex* gives English a third family of derivatives. *Sextet* — a group of six. *Sextant* — the navigational instrument that measures a sixth of a circle (60°). *Semester* — from Latin *semestris*, a contraction of *sex mēnsis*, 'six months'.
Three surface forms — *six*, *hexa-*, *sex-* — one ancestral root *\*swéḱs*.
The Sistine Chapel
The Sistine Chapel — *Cappella Sistina* — is named after Pope Sixtus IV, who commissioned its construction in the 1470s. The papal name *Sixtus* derives from Latin *sextus*, 'sixth', itself directly from *sex*. The chapel Michelangelo painted is, etymologically, the 'Sixth Chapel'. Every art history student who stands under the Creation of Adam is standing inside a PIE numeral.
Why Numerals Matter
Franz Bopp used the regularity of nominal and verbal paradigms to establish the kinship of Sanskrit, Persian, Greek, Latin, and Germanic. Numerals formed a crucial part of that evidence. A shared verb paradigm might conceivably reflect contact. A shared counting system, preserved across ten thousand years of separation, in cultures with no historical contact — that requires a common ancestor.
Low numerals — one through ten — are the most conservative stratum of any vocabulary. They are learned in early childhood, used constantly, rarely replaced by borrowing, and subject to powerful social pressure toward conformity. When the same word for 'six' appears in an Iron Age inscription from Italy, a medieval Welsh manuscript, a Vedic hymn, and a modern Lithuanian parish register, the comparative method is not inferring history — it is reading it.