Tonal and stress accents

[Anthony Appleyard]

  Jens Elmegaard Rasmussen <jer at cphling.dk> wrote about IE stress.

  The image that I had was this: IE originally has a pitch accent, and it had
no zero-grading, and the IE-speakers hunted on foot on the steppes. They
domesticated animals including the horse, and that lead them into a period of
expansion; as they absorbed speakers of other languages around, foreign
influences including stress accent got in. Pitch accent later reasserted
itself, but while the stress accent was current, zero-grading came in by the
common weakening of unstressed vowels. Before that, word forms that are
distinguished by zero grade / normal grade in classical IE were distinguished
by accent only: {!elEIqwom} = "I was leaving"; {!eleiqwOm} > {!eliqwOm} = "I
left".

  Some of the other peoples absorbed in that time likely had no laryngeals in
their own old languages, and that may be why later IE often lost laryngeals.