Editing Grimm's law (section)

==Overview==
Grimm's law consists of three parts, forming consecutive phases in the sense of a [[chain shift]].<ref>{{cite book |last=Campbell |first=Lyle |title=Historical linguistics | edition=2nd |publisher=MIT Press |location=Cambridge |year=2004 |isbn=0-262-53267-0 |pages=49}}</ref> The phases are usually constructed as follows:

# Proto-Indo-European voiceless [[stop consonant|stop]]s change into Proto-Germanic [[voicelessness|voiceless]] [[fricatives]].
# Proto-Indo-European voiced stops become Proto-Germanic [[Voicelessness#Lack of voicing contrast in obstruents|voiceless stops]].
# Proto-Indo-European voiced aspirated stops become  Proto-Germanic voiced stops or fricatives (as [[allophone]]s).

This chain shift (in the order 3, 2, 1) can be abstractly represented as:

* {{PIE|bʰ}} → {{PIE|b}} → {{PIE|p}} → ɸ
* {{PIE|dʰ}} → {{PIE|d}} → {{PIE|t}} → {{PIE|θ}}
* {{PIE|gʰ}} → {{PIE|g}} → {{PIE|k}} → {{PIE|x}}
* {{PIE|gʷʰ}} → {{PIE|gʷ}} → {{PIE|kʷ}} → {{PIE|xʷ}}

Here each sound moves one position to the right to take on its new sound value. Within Proto-Germanic, the sounds denoted by {{angbr|b}}, {{angbr|d}}, {{angbr|g}} and {{angbr|gw}} were stops in some environments and fricatives in others, so {{PIE|bʰ}} → {{PIE|b}} indicates {{PIE|bʰ}} → {{PIE|b/β}}, and likewise for the others. The voiceless fricatives are customarily spelled {{angbr|f}}, {{angbr|þ}}, {{angbr|h}} and {{angbr|hw}} in the context of Germanic.

The exact details of the shift are unknown, and it may have progressed in a variety of ways before arriving at the final situation. The three stages listed above show the progression of a "pull chain", in which each change leaves a "gap" in the phonological system that "pulls" other phonemes into it to fill the gap. Alternatively, the shift may have occurred as a “push chain”, where the sounds changed in reverse order, with each change "pushing" the next forward to avoid merging the phonemes.

The steps could also have occurred somewhat differently. Another possible sequence of events could have been:

# Voiceless stops are allophonically aspirated under most conditions.
# Voiced stops become unaspirated voiceless stops.
# All aspirated stops become fricatives.

This sequence would lead to the same result. This variety of Grimm's law is often suggested in the context of Proto-Indo-European [[glottalic theory]], which is followed by a minority of linguists. This theoretical framework assumes that PIE "voiced stops" were actually voiceless to begin with, so that the second phase did not actually exist as such, or was not actually devoicing but was losing some other articulatory feature like [[glottalization]] or [[ejective]]ness. This alternative sequence also accounts for [[Verner's law]] phonetics (see below), which are easier to explain within the glottalic theory framework when Grimm's law is formulated in this manner.

Additionally, aspirated stops are known to have changed to fricatives when transiting between Proto-Indo-European and [[Proto-Italic]], so representing a plausible potential change from Proto-Indo-European to Proto-Germanic.