Indo-European sound laws

Template:PIE notice As the Proto-Indo-European language (PIE) broke up, its sound system diverged as well, according to various sound laws in the daughter Indo-European languages.

Especially notable is the palatalization that produced the satem languages, along with the associated ruki sound law. Other notable changes are Grimm's law and Verner's law in Proto-Germanic; an independent change similar to Grimm's law in Armenian; loss of prevocalic *p- in Proto-Celtic; Brugmann's law in Proto-Indo-Iranian; Winter's law and Hirt's law in Balto-Slavic; and merging of voiced and breathy-voiced stops, and /a/ and /o/, in various "northern" languages. Bartholomae's law in Indo-Iranian, and Sievers' law in Proto-Germanic and (to some extent) various other branches, may or may not have been common Indo-European features. A number of innovations, both phonological and morphological, represent areal features common to the Italic and Celtic languages; among them are the development of labiovelars to labial consonants in some Italic and Celtic branches, producing "p-Celtic" and "q-Celtic" languages (likewise "p-Italic" and "q-Italic", although these terms are less used). Another grouping with many shared areal innovations is Greek, Indo-Iranian, and Armenian; among the common phonological innovations are Grassmann's law in Greek and Indo-Iranian, and weakening of pre-vocalic /s/ to /h/ in Greek, Iranian and Armenian.

Consonants

The following table shows the Proto-Indo-European consonants and their reflexes in selected Indo-European daughter languages. Background and further details can be found in various related articles, including Proto-Indo-European phonology, Centum and satem languages, the articles on the various sound laws referred to in the introduction, and the articles on the various IE proto-languages, language groups and language phonologies. For development of the laryngeals and syllabic consonants, see the vowels table below.

Table 1. Reflexes of Proto-Indo-European single consonants
PIE	Indo-Iranian		Balto-Slavic		Alb.	Arm.	Anatol.	Toch.	Greek		Italic	Celtic		Germanic
	Skr.	Av.	O.C.S.	Lith.			Hitt.		Greek		Latin	Old Irish		Gothic	English
	Skr.	Av.	O.C.S.	Lith.			Hitt.		normal	C+[j]	Latin	normal	-C-⁸	Gothic	English
*p	p; ph [pʰ] ^{[C 1]}	p; f¹⁷	p			h; w ^{[C 2]}	p			pt	p	Ø		f; b [β] ^{[C 3]}	f; v, f⁸
*t	t; th [t̪ʰ] ^{[C 1]}	t; θ¹⁷	t			tʿ [tʰ]	t; z [ts] ^{[C 4]}	t; c [c] ^{[C 4]}	t	s; tt/ss^{[C 2]}	t	t	th [θ]	þ [θ]; d [ð]; ^{[C 3]}	th; d; ^{[C 3]}
*ḱ	ś [ɕ]	s		š [ʃ]	th [θ]; k⁹	s	k	k; ś [ɕ]⁹	k		c [k]	c [k]	ch [x]	h; g [ɣ] ^{[C 3]}	h; Ø;⁸ y ^{[C 3]}
*k	k; c [t͡ɕ]; ^{[C 4]} kh [kʰ] ^{[C 1]}	k; c [tʃ]; ^{[C 4]} x¹⁷	k; č [tʃ]; ^{[C 4]} c [ts]¹⁰	k	k	kʿ [kʰ]	k		k		c [k]			h; g [ɣ] ^{[C 3]}	h; Ø;⁸ y ^{[C 3]}
*kʷ	k; c [t͡ɕ]; ^{[C 4]} kh [kʰ] ^{[C 1]}	k; c [tʃ]; ^{[C 4]} x¹⁷	k; č [tʃ]; ^{[C 4]} c [ts]¹⁰	k	k; s; ^{[C 4]} q [c]¹⁰	kʿ [kʰ]	ku		p; t; ^{[C 4]} k⁶		qu [kʷ]; c [k] ^{[C 5]}			ƕ [ʍ]; gw, w ^{[C 3]}	wh; w ^{[C 3]}
*b	b; bh ^{[C 1]}	b; β ^{[C 6]}	b			p			b	pt	b	b [b]	-[β]-	p
*d	d; dh ^{[C 1]}	d; δ ^{[C 6]}	d		d; dh [ð]⁸	t		ts; ś [ɕ] ^{[C 4]}	d	z [zd] > [z]	d	d [d]	-[ð]-	t
*ǵ	j [d͡ʑ]; h [ɦ] ^{[C 1]}	z		ž [ʒ]	dh [ð]; g⁹	c [ts]	k	k; ś [ɕ]⁹	g		g	g [ɡ]	-[ɣ]-	k	c / k; ch¹⁰
*g	g; j [d͡ʑ]; ^{[C 4]} gh; ^{[C 1]} h [ɦ] ^{[C 1]} ⁵	g; j [dʒ]; ^{[C 4]} γ ^{[C 6]}	g; ž [ʒ]; ^{[C 4]} dz¹⁰	g	g	k	k		g		g	g [ɡ]	-[ɣ]-	k	c / k; ch¹⁰
*gʷ	g; j [d͡ʑ]; ^{[C 4]} gh; ^{[C 1]} h [ɦ] ^{[C 1]} ⁵	g; j [dʒ]; ^{[C 4]} γ ^{[C 6]}	g; ž [ʒ]; ^{[C 4]} dz¹⁰	g	g; z; ^{[C 4]} gj [ɟ]¹⁰	k	ku		b; d; ^{[C 4]} g⁶		u [w > v]; gu [ɡʷ] ^{[C 7]}	b [b]	-[β]-	q [kʷ]	qu
*bʰ	bh [bʱ]	b; β ^{[C 6]}	b			b; w⁸	p		ph [pʰ]	pt	f;²¹ b	b [b]	-[β]-	b [b]; b [β];⁸ f ^{[C 8]}	b; v / f²⁴
*dʰ	dh [dʱ]	d; δ ^{[C 6]}	d				t	t; c [c] ^{[C 4]}	th [tʰ]	tt/ss	f;²¹ d; b ^{[C 9]}	d [d]	-[ð]-	d; d [ð];⁸ þ ^{[C 8]}	d
*ǵʰ	h [ɦ]	z		ž [ʒ]	dh [ð]; d⁹	j [dz]; z⁸	k	k; ś [ɕ] ^{[C 4]}	kh [kʰ]		h; h / g⁹	g [ɡ]	-[ɣ]-	g; g [ɣ];⁸ g [x] ^{[C 8]}	g; y / w²⁴
*gʰ	gh [ɡʱ]; h [ɦ] ^{[C 4]}	g; j [dʒ]; ^{[C 4]} γ ^{[C 6]}	g; ž [ʒ]; ^{[C 4]} dz¹⁰	g	g	g; ǰ [dʒ] ^{[C 4]}	k		kh [kʰ]		h; h / g⁹			g; g [ɣ];⁸ g [x] ^{[C 8]}	g; y / w²⁴
*gʷʰ	gh [ɡʱ]; h [ɦ] ^{[C 4]}	g; j [dʒ]; ^{[C 4]} γ ^{[C 6]}	g; ž [ʒ]; ^{[C 4]} dz¹⁰	g	g; z; ^{[C 4]} gj [ɟ]¹⁰	g; ǰ [dʒ] ^{[C 4]}	ku		ph [pʰ]; th [tʰ]; ^{[C 4]} kh [kʰ]⁶		f;²¹ g / u [w];⁸ gu [ɡʷ] ^{[C 7]}			g; b;²¹ w;⁸ gw ^{[C 7]}	g; b;²¹ w⁸
*s	s	h [h, x]	s		sh [ʃ]; gj [ɟ];¹² h⁸	h; Ø⁸	š [s]	s; ṣ [ʂ]	h;²¹ s;^{22, 13} Ø;⁸ [¯] ^{[C 10]}	i	s; r⁸	s [s]	-[h]-	s; z ^{[C 3]}	s; r ^{[C 3]}
*s	ṣ [ʂ]¹¹	š [ʃ]¹¹	x [x]¹¹	š [ʃ]¹¹	sh [ʃ]; gj [ɟ];¹² h⁸	h; Ø⁸	š [s]	s; ṣ [ʂ]	h;²¹ s;^{22, 13} Ø;⁸ [¯] ^{[C 10]}	i	s; r⁸	s [s]	-[h]-	s; z ^{[C 3]}	s; r ^{[C 3]}
*m	m									in	m	m [m]	-[w̃]-	m
*-m ^{[C 8]}	m		˛ [˜]	n		Ø		n		--	m	n		Ø
*n	n		n; ˛ [˜] ^{[C 8]}	n				n; ñ [ɲ]	n	in	n
*l	r (dial. l)	r	l		l; ll [ɫ]⁸	l / ɫ [ɫ > ɣ]	l			il	l
*r	r				r [ɾ]; rr [r]⁸	r				ir	r
*i̯	y [j]		j [j]		gj [ɟ]; Ø	Ø	y [j]		z [zd] > [z] / h; Ø ⁸	?i	i [j]; Ø ⁸	Ø		j	y
*u̯	v [ʋ]	v [w]	v	v [ʋ]	v	g / w	w		w > h / Ø	i	u [w > v]	f	-Ø-	w
PIE	Skr.	Av.	O.C.S.	Lith.	Alb.	Arm.	Hitt.	Toch.	Greek	Greek+/j/	Latin	Old Irish		Gothic	English

Notes for table 1:

^ ^a ^b ^c ^d ^e ^f ^g ^h Before an original laryngeal.
^ ^a ^b After a vowel.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Following an unstressed vowel (Verner's law).
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u Before a (PIE) front vowel (*i, *e).
^ Before or after a (PIE) rounded vowel (*u, *o).
^ ^a ^b ^c ^d ^e ^f In Younger Avestan, after a vowel.
^ ^a ^b ^c After n.
^ ^a ^b ^c ^d ^e At the end of a word.
^ After u, r or before r, l.
^ Before or after a resonant (r, l, m, n).

Consonant clusters

Proto-Indo-European also had numerous consonant clusters, such as *st, *ḱs. In most cases in most languages, each consonant in a cluster develops according to the normal development given in the table above. Many consonant clusters however also show special developments in multiple languages. Some of these are given by the following table (with cases of otherwise predictable development in gray):

Table 2. Reflexes of Proto-Indo-European consonant clusters
PIE	Indo-Iranian		Balto-Slavic		Alb.	Arm.	Anatol.	Toch.	Greek		Italic	Celtic	Germanic
	Skr.	Av.	O.C.S.	Lith.			Hitt.		Greek		Latin	Old Irish	Gothic	English
	Skr.	Av.	O.C.S.	Lith.			Hitt.		normal	C+[j]	Latin	Old Irish	Gothic	English
*sp	sp	sp ^{[CC 1]}	sp		f	sp ^{[CC 1]} / pʿ [pʰ]	normal dev.		sp ^{[CC 1]}	?	sp	f	sp ^{[CC 2]}
*st	st	st ^{[CC 1]}	st		sht [ʃt]	st ^{[CC 1]}	normal dev.		st ^{[CC 1]}	s; tt/ss^{[CC 3]}	st		st ^{[CC 2]}
*sḱ	ch [t͡ɕʰ]; cch^{[CC 3]}	s?	sk	š?	h	?? č`; c`^{[CC 3]}	normal dev.		sk; ^{[CC 1]} kh [kʰ];¹⁹ skh [skʰ] ^{[CC 4]}		sc [sk]	sc [sk]	sk ^{[CC 2]}	sh [ʃ]
*sk	sk, sc	sk, sč ^{[CC 1]}	normal dev.		?	sk ^{[CC 1]}	normal dev.		sk; ^{[CC 1]} kh [kʰ];¹⁹ skh [skʰ] ^{[CC 4]}		sc [sk]		sk ^{[CC 2]}
*skʷ	sk, sc	sk, sč ^{[CC 1]}	normal dev.		?	sk ^{[CC 1]}	normal dev.		norm.		squ [skʷ]		sq ^{[CC 2]}
*t+t [tst]	tt; tth ^{[CC 5]}	st; sθ¹⁷?	st		s	s?	zt [tst]	ss?	st		ss		ss / st
*pt	pt	ft			t				pt		pt	cht [xt]	ft ^{[CC 2]}
*ḱt	ṣṭ [ʂʈ]	št [ʃt]							kt		ct [kt]		ht ^{[CC 2]}	ght [t] ^{[CC 2]}
*kt	kt	xt							kt		ct [kt]
*kʷt	kt	xt							pt		ct [kt]
*ps									ps		ps	s, ss	fs	ps
*ḱs	kṣ	š			sh [ʃ]				ks		x [ks]		hs	x [ks]
*ks	kṣ¹¹	xš¹¹						(ks)	ks		x [ks]		hs
*kʷs	kṣ¹¹	xš¹¹					kʷs		ps		x [ks]
PIE	Skr.	Av.	O.C.S.	Lith.	Alb.	Arm.	Hitt.	Toch.	Greek	Greek+/j/	Latin	Old Irish	Gothic	English

Notes to Table 2:

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ In contrast to *s normally giving h in Avestan, Armenian and Greek.
^ ^a ^b ^c ^d ^e ^f ^g Germanic spirant law: *p, *t, *k, *kʷ remain stops when preceded by another stop or *s.
^ ^a ^b ^c Between vowels.
^ After (Greek) th. ^{[clarification needed]}
^ Before an original laryngeal.

Notes:

⁶ Before or after a (PIE) u.
⁸ Between vowels.
⁹ Before a sonorant.
¹⁰ Before secondary (post-PIE) front-vowels.
¹¹ After r, u, k, i (Ruki sound law).
¹² Before a stressed vowel.
¹⁷ Before a consonant or original laryngeal.
¹⁹ After r, l, m, n, t, d, possibly other consonants?
²¹ At the beginning of a word.
²² Before or after an obstruent (p, t, k, etc.; s).
²⁴ Between vowels, or between a vowel and r, l (on either side).

Vowels and syllabic consonants

This table shows the Proto-Indo-European vowels and syllabic consonants (as reconstructed both before and after the acceptance of laryngeal theory), and their reflexes in selected Indo-European daughter languages. Background and further details can be found in various related articles, including Proto-Indo-European phonology, the articles on the various sound laws referred to in the introduction, and the articles on the various IE proto-languages, language groups and language phonologies.

Trad. PIE	Laryng. PIE	Skr.	Av.	O.C.S.	Lith.	Arm.	Alb.	Toch.	Hitt.	Greek	Latin¹⁸	Proto-Celtic	Gothic¹⁹	Old English¹⁸
Trad. PIE	Laryng. PIE	Skr.	Av.	O.C.S.	Lith.	Arm.	Alb.	Toch.	Hitt.	Greek	Latin¹⁸	Proto-Celtic	Gothic¹⁹	normal	umlauted²⁰
*e	e, h₁e	a		e			je, ie, e, i; ja¹²	ä	e, i	e			i; aí [ɛ]²	e; eo²¹	i; ie²¹
*a	(a³), h₂e			o	a	a	ha, a	ā	ha, a	a			a	æ; a;²² ea²¹	e; ie²¹
*o	*h₃e					o, a	a	a, e	a	o
*o	*o	a; ā⁴				o, a		a, e	a	o
*ə¹⁶	*h₁¹⁶	i	i, Ø	Ø		a, Ø		ā	a	e	a		a, Ø
	*h₂¹⁶								h	a
	*h₃¹⁶									o
*-	*h₁-¹⁷	Ø				e (a?)	Ø		a	e (o)	Ø
	*h₂-¹⁷					a			ha	a
	*h₃-¹⁷					a			a, ha	o
*ē	ē, eh₁	ā		ě	ė	i	o, ua	a/e?; ā?⁸	e, i	ē		ī	ē	ǣ
*ā	(ā³), eh₂			a	o [oː]	a	o, ua	a/o?	a, ah	ā > ē¹⁵	ā	ā	ō		ē
*ō	ō, eh₃			a	uo	u	e	a/ā?; ū?⁸	a	ō		ā; ū⁸	ō		ē
*i	*i	i		ь	i	i	i; e¹⁰	ä	i	i			i; aí [ɛ]²	i
*ī	*ih₁	ī		i	y [iː]	i	i	i		ī	ī		ei [iː]	ī
	*ih₂					i or ^(j)a?⁷		yā		ī or ^(j)ā?⁷
	*ih₃					i or ^(j)a?⁷		yā		ī or ^(j)ō?⁷
*ei	ei, h₁ei	ai > ē	ai > ōi, āi > aē⁴		ei; ie⁵	i		e	ei	ei	ī	īa; ē⁶
*oi	oi, h₃ei			ě	ai; ie⁵	e	e, ai		ay	oi	ū	oe	ái	ā	ǣ
*ai	(ai³), h₂ei			ě	ai; ie⁵	e	e, ai		ay	ai	ae	ae	ái	ā	ǣ
*ēi	*ēi	āi; ā⁸	āi; ā(i)⁸	i			i			ēi	ī?		ei [iː]	ī
*ōi	ōi (oei)			y; u⁸	ai; ui⁸		e, ai		ai	ōi	ō	u⁸	ái	ā	ǣ
*āi	*eh₂ei			ě			e, ai			āi > ēi¹⁵	ae		ái	ā	ǣ
*u	*u	u		ъ	u	u	u; y¹¹	ä	u	u	u	u; o¹	u; aú [ɔ]²	u; o²³	y
*ū	*uh₁	ū		y	ū	u	y; i⁸	u		ū	ū				ȳ
	*uh₂					u or ^(w)a?⁷		wā		ū or ^(w)ā?⁷
	*uh₃					u or ^(w)a?⁷		wā		ū or ^(w)ō?⁷
*eu	eu, h₁eu	ō	ə̄u; ao⁴	ju	iau	oy	e	u		eu	ū	ūa; ō⁹	iu	ēo	īe
*ou	ou,h₃eu			u	au	oy	a	o, au		ou	ū		áu	ēa
*au	(au³), h₂eu			u	au	aw	a	o, au		au	au		áu	ēa
*ēu	*ēu	āu		u	iau		e				ū?		iu	ēo
*ōu	*ōu	āu					a			ō			áu	ēa
*m̥	*m̥	a		ę	im̃; um̃¹⁴	am	a	äm	am	a	em	em, am	um	um	ym
*m̥̅	*mh₁	ā			ìm; ùm¹⁴	ama		mā		mē	mā
	*mh₂									mā > mē¹⁵
	*mh₃									mō
*m̥m	*m̥m	am		ьm/ъm	im; um¹⁴	am				am	em	am
*n̥	*n̥	a		ę	iñ; uñ¹⁴	an		än	an	a	en	en, an	un	un	yn
*n̥̄	*nh₁	ā			ìn; ùn¹⁴	ana		nā		nē	nā
	*nh₂									nā > nē ¹⁵
	*nh₃									nō
*n̥n	*n̥n	an		ьn/ъn	iñ; uñ¹⁴	an				an	en	an
*l̥	*l̥	ṛ	ərə	lь/lъ	il̃; ul̃¹⁴	al	il, li; ul, lu	äl	al	la	ol	li²⁴; al	ul	ul; ol²³	yl
*l̥̄	*lh₁	īr; ūr¹³	arə		ìl; ùl¹⁴	ala	al	lā		lē	lā
	*lh₂									lā > lē¹⁵
	*lh₃									lō
*l̥l	*l̥l	ir; ur¹³	ar	ьl/ъl	il; ul¹⁴	al, la				al	el	al
*r̥	*r̥	ṛ	ərə	rь/rъ	ir̃; ur̃¹⁴	ar	ir, ri; ur, ru	är	ar	ra	or	ri²⁴; ar	aúr [ɔr]	ur; or²³	yr
*r̥̄	*rh₁	īr; ūr¹³	arə		ìr; ùr¹⁴	ara	ra	rā		rē	rā
	*rh₂									rā > rē¹⁵
	*rh₃									rō
*r̥r	*r̥r	ir; ur¹³	ar	ьr/ъr	ir; ur¹⁴	ar				ar	ar	ar
Trad. PIE	Laryng. PIE	Skr.	Av.	O.C.S.	Lith.	Arm.	Alb.	Toch.	Hitt.	Greek	Latin¹⁸	Proto-Celtic	Gothic¹⁹	normal	umlauted²⁰
Trad. PIE	Laryng. PIE	Skr.	Av.	O.C.S.	Lith.	Arm.	Alb.	Toch.	Hitt.	Greek	Latin¹⁸	Proto-Celtic	Gothic¹⁹	Old English¹⁸

Notes

¹ Before wa.
² Before r, h. Gothic, but not other Germanic languages, merges /e/ and /i/.
³ The existence of PIE non-allophonic a is disputed.
⁴ In open syllables (Brugmann's law).
⁵ Under stress.
⁶ Before palatal consonants.
⁷ The so-called breaking is disputed (typical examples are *proti-h₃kʷo- > Ved. prátīkam ~ Gk. πρόσωπον; *gʷih₃u̯o- > Ved. jīvá- ~ Arm. keank‘, Gk. ζωός; *duh₂ro- > Ved. dūrá- ~ Arm. erkar, Gk. δηρός)
⁸ In a final syllable.
⁹ Before velars and unstressed
¹⁰ Before ā in the following syllable.
¹¹ Before i in the following syllable.
¹² In a closed syllable.
¹³ In the neighbourhood of labials.
¹⁴ In the neighbourhood of labiovelars.
¹⁵ ā > ē in Attic and Ionic dialects only.
¹⁶ Between consonants, or at the end of a word after a consonant.
¹⁷ At the beginning of a word, followed by a consonant.
¹⁸ In initial syllables only.
¹⁹ In non-final syllables only.
²⁰ Before i, ī, or /j/ in the next syllable in Proto-Germanic (i-umlaut).
²¹ Before h, w, or before r, l plus a consonant ("breaking").
²² Before a back vowel in the next syllable (a restoration).
²³ Before a non-high vowel in the next syllable (a-mutation).
²⁴ Before a stop or m.

Examples

See the list of Proto-Indo-European roots hosted at Wiktionary.

*p

*pṓds, ~ *ped-, "foot".^[1]

Vedic Sanskrit: pád-
Avestan: pâdha
Slovenian: pòd, "floor"
Lithuanian: pėda, "foot bottom"
Armenian: otn
Tocharian: A pe, B pai
Luwian: pa-da-, pa-ta-
Greek: poús, podós
Latin: pēs, pedis
Scottish Gaelic: edh, "pace"
Gothic: fotus (*p -> f by Grimm's Law)

*t

*tréyes, "three".^[1]

Vedic Sanskrit: tráyas
OCS: trьje
Lithuanian: trỹs
Albanian: tre
Greek: treĩs
Latin: trēs
Irish: trí
Arm.ere
Old Norse: þrir (*t -> þ by Grimm's Law)

*ḱ

*ḱm̥tóm, "hundred" (from earlier *dk̂m̥tóm)^[1]

Vedic Sanskrit: śatám
Later Avestan: satəm
OCS: sьto
Lithuanian: šimtas
Tocharian: A känt, B känte
Greek: hekatón
Latin: centum (i.e., kentum)
Welsh: cant
Gothic: hund- (from proto-Germanic *xund)^[2]

*k

*kreuh₂, "raw flesh"^[1]

Vedic Sanskrit: kravíṣ-, "raw meat"
Lithuanian: kraûjas, "blood"
OCS: krьvь, "blood"
Greek: kréas, "meat"
Latin: cruor, "raw blood"
Irish: cró, "blood, gore"
Old English: hrō, "raw"

Sound laws within PIE

A few phonological laws can be reconstructed that may have been effective prior to the final breakup of PIE by internal reconstruction.

Sievers' law (Edgerton's law, Lindeman's option)
Bartholomae's law
Szemerényi's law
Stang's law
Siebs' law

References

^ ^a ^b ^c ^d Meier-Brügger, Michael; Gertmenian, Charles (translator) (2003). Indo-European linguistics. Berlin [u.a.]: de Gruyter. pp. 101–131. ISBN 3-11-017433-2. {{cite book}}: |first2= has generic name (help)
^ Hock, Hans Heinrich (1986). Principles of historical linguistics. Berlin; New York: Walter de Gruyter. p. 132. ISBN 3-11-010600-0.

[P+H-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h Before an original laryngeal.

[VCV-2] After a vowel.

[Verner-3] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Following an unstressed vowel (Verner's law).

[Cie-4] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u Before a (PIE) front vowel (*i, *e).

[5] Before or after a (PIE) rounded vowel (*u, *o).

[YAv-6] ^ ^a ^b ^c ^d ^e ^f In Younger Avestan, after a vowel.

[ngw-7] After n.

[final-8] At the end of a word.

[9] After u, r or before r, l.

[10] Before or after a resonant (r, l, m, n).

[noh-11] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ In contrast to *s normally giving h in Avestan, Armenian and Greek.

[GSL-12] ^ ^a ^b ^c ^d ^e ^f ^g Germanic spirant law: *p, *t, *k, *kʷ remain stops when preceded by another stop or *s.

[VCV-13] Between vowels.

[14] After (Greek) th. ^{[clarification needed]}

[P+H-15] Before an original laryngeal.

[m-b-16] Meier-Brügger, Michael; Gertmenian, Charles (translator) (2003). Indo-European linguistics. Berlin [u.a.]: de Gruyter. pp. 101–131. ISBN 3-11-017433-2. {{cite book}}: |first2= has generic name (help)

[17] Hock, Hans Heinrich (1986). Principles of historical linguistics. Berlin; New York: Walter de Gruyter. p. 132. ISBN 3-11-010600-0.

[C 1]

[C 2]

[C 3]

[C 4]

[C 5]

[C 6]

[C 7]

[C 8]

[C 9]

[C 10]

[CC 1]

[CC 2]

[CC 3]

[CC 4]

[CC 5]

[1]

[2]

v t e Proto-Indo-European language
Phonology	Accent Centum and satem Glottalic theory Laryngeal theory s-mobile Sound laws boukólos rule *kʷetwóres rule Glossary of sound laws Brugmann's Bartholomae's Fortunatov's Grassmann's Osthoff's Pinault's Siebs's Sievers's (Edgerton's converse) Stang's Szemerényi's Weise's
Morphology	Ablaut Caland system h₂e-conjugation Narten present Nasal infix Root Thematic vowel Vṛddhi
Parts of speech	Nominals (nouns and adjectives) Numerals Particles Pronouns Verbs copula Vocabulary
Main sources	Indogermanisches etymologisches Wörterbuch (IEW) Lexikon der indogermanischen Verben (LIV) Lexikon der indogermanischen Partikeln und Pronominalstämme (LIPP) Nomina im Indogermanischen Lexikon (NIL) Indo-European Etymological Dictionary (IEED)
Origins	Indo-European migrations Proto-Indo-European homeland Salmon problem
Artificial compositions	Schleicher's fable The king and the god
Theories	Kurgan hypothesis Schleicher theories Anatolian hypothesis Armenian hypothesis Outdated theories: Beech argument North European hypothesis
See also	Proto-Indo-European mythology Proto-Indo-European society Indo-European studies Encyclopedia of Indo-European Culture (EIE)