The evolution of Resian into such a distinct dialect happened gradually and in three stages. The first stage lasted until the 14th century; at that time, Resian was mostly influenced by the Gail Valley dialect. In the second stage, it acquired many features of Venetian Slovene dialects and other Littoral dialects. The third stage represents changes that are unique to Resian and cannot be found elsewhere.
First stage Until the 13th century, Resian experienced the same evolution as all other Slovene dialects, forming into Alpine Slovene. It was part of the northwestern dialect because long yat diphthongized into *
ie and long *
ō diphthongized into *
uo. It did not experience
denasalization of nasal vowels. After further division, it fell into the category of the northern dialect, the same as other Carinthian dialects and unlike other Littoral dialects. It thus did not experience lengthening of non-final vowels at that time, because vowel lengthening in northern dialects happened only after the 16th century, well past the point when Resian lost contact with the Carinthian dialects and leading to possible different reflexes for formerly long and short vowels. Long *
ə̄ also turned into *
ē, which is unique to Resian in comparison to other Littoral dialects because there it turned into *
a. The evolution then continued the same as with other Carinthian dialects, leading to the Carinthian dialect base. Short non-final *
ě̀, *
ò, and
è evolved differently from their long counterparts, into *
é,
ó, and
é, respectively. Long *
ē turned into *
ẹ̄, whereas the nasal vowels remained intact and only lengthened. Long *
ə̄ turned into a very open
ȩ̄ and short non-final vowels lengthened. Later, Resian followed the same patterns as the Jaun Valley dialect, such as *
ie and *
uo simplifying into *
iə and *
uə, *
é and
ó turned into *
ẹ and *
ọ, and the > accent shift, as well as the merger of *
ē and *
ě̄. Long nasal vowels also denasalized and *
ę̄ merged with *
ə̄, resulting in *
ē and *
ō.
Second stage The second stage was primarily influenced by the Torre Valley dialect. Open *
ē and *ō became close-mid *
ẹ̄2 and *
ọ̄2 (in contrast to previously existing *
ẹ̄1 and *
ọ̄1). Short *
ə turned into *a, *
ĺ turned into *
i̯, *
w started turning into *
v before front vowels, and *
ł turned into *
l. This connection also hindered some developments, such as *
t →
č, the > shift, and the > shift, which are present today in the Gail Valley dialect, but not in Resian. Final -
m in most cases also turned into -
n, a feature that also appeared in the Gail Valley dialect. The dialect also devoiced all final
obstruents.
Third stage Resian lost both tonal and length oppositions, which is unlike any neighboring dialect. The diphthongs *
iə and *
uə monophthongized into *
í2 and *
ú2, respectively, forming a vowel system without diphthongs, another feature of Resian not seen in any neighboring dialects. The vowels *
ọ́1 and *
ẹ́1 turned into
o̤ and
e̤, which might have actually happened before *
ọ́2 and *
ẹ́2. Now only *
ọ́ and *
ẹ́ turned into *
i and *
u near a nasal consonant. Other changes did not cover the entire territory. The vowels *
í1 and *
ú1 from previously longer syllables turned into
i̤ and
ṳ, except in San Giorno (), where previously short *
í1 and *
ú1 turned into centralized vowels, whereas elsewhere they turned into
e and
o. Syllabic *
ł̥́ mostly turned into
ol, except in Oseacco () and Uccea (), where it turned into
ú. The consonant *
ɣ then turned into
h, or even disappeared. Other changes are specific to each microdialect. == Morphology ==