Proto-West Persian'

The branch further divides into the Bustaxoid and Tsonboid languages.

Changes from Proto-Persian'

• high vowels
  • ɪ ʊ ɪː ʊː → i u əj əw
  • ɪw ɪj ʊj → iw iː uj
• loss of difthongs in _w
  • k → kʷ / w_C
  • iw → yː
  • ew → e₂ː
  • æw → æː
  • ow → uː
  • əw → o₁ː
• stop phonation/MOA changes
  • intervocalic lenition: b d → β ð
  • intervocalic voicing: p t k q → b d ɡ ɢ
  • loss of aspiration
    • ʰp ʰt ʰk(ʷ) ʰq → p t k(ʷ) q
    • pʰ tʰ kʰ qʰ → ɸ θ x χ
  • stop clusters with a 2nd voiced member become voiced thruout
• lo vowels
  • æ ɐ æː ɒː → a ə aː o₂ː

Intermediate form

Consonants

p	t			k	kʷ	q
b	d			ɡ	ɡʷ	ɢ
ɸ	θ	s	ɬ	x	xʷ	χ	h
β	ð					ʁ
m	n	r	l	j	w

No evidence exists of labialized uvulars.

/ɸ θ x xʷ/ could not occur intervocally, while /β ð/ could only occur there, thereby best being analyzable as allophones of their unvoiced counterparts.

Carrying over from Proto-Persian' was the feature that both nasals could occur before just about any consonants, apparently without any POA assimilation taking place. The existence of a separate, prenasal onglide for the folloing consonant has been proposed.

Vowels

The short vowel inventory is /i u e ə o a/, the long vowel inventory /iː yː uː eː oː aː/.

Two distinct types of /eː oː/ are reconstructed for PWP'. Most likely these are /eː oː/ and /ɛː ɔː/, but it remains unclear which are which. An alternate theory proposes /øː ɤː/ insted but with little additional clarification.