Consonants

Middle Polish's consonant system differs little from Old Polish's.

The clusters ir/irz/yr/yrz lowered to ér/érz and ultimately to er/erz.

czyrwony > czérwony > czerwony ^[8]

Similarly, the clusters il/ił/yl/ył sporadically and non-permanently lowered to el/eł.

był > beł ^[8]

There was also a tendency for prenasal raising.^[9]

lepiánka > lepionka

tam>tąm

dom > dóm

nasienie > nasinie

Or, conversely, sometimes vowels lowered.

słuńce > słońce

One major change was a depalatalization of the consonants /t͡sʲ/, /d͡zʲ/, /t͡ʃ/, /d͡ʒ/, /ʃ/, and /ʒ/ to /t͡s/, /d͡z/, /t͡ʂ/, /d͡ʐ/, /ʂ/, and /ʐ/ respectively.

The consonant /rʲ/ also underwent depalatalization, going from /rʲ/ to /rʐ/, to /ʐ/ by the end of the sixteenth century.^[10]

Labials underwent depalatalization in coda position.^[10]

At the turn of 17th century L-vocalization begins, ultimately finishing in the Modern Polish era.^[11]

There was some wavering as to the softness of sibilants, as well.

ślak/szlak

prozno/prożno

snicerz/sznicerz

synogarlica/sinogarlica^[11]

The final consonant system at the end of the Middle Polish period was thus:

Vowels

Middle Polish inherited Old Polish's late vowel system.^[12]

At first there were two groups of vowels, so-called "clear" (Polish "jasny") vowels (transcribed /a, ɛ, i, ɔ, u, ɨ/) and the so-called "pitched" (Polish "pochylony") vowels (transcribed /ɒ, e, o/), which arose from Old Polish long vowels.

There was a tendency for the pitched vowels to merge with some neighboring non-pitched vowel.

é > e/y/i rzékę > rzekę, dobrémi > dobrymi^[13]

á > a mám > mam^[14]

ó > u (still) written ó skóra > skóra (used in poetry to rhyme with dziura)^[15]

Nasal /æ̃~ɛ̃/ raised and fronted to /ɛ̃/, whereas /ɒ̃~ɔ̃/ raised and back to /ɔ̃/, however there was some irregular shifting of nasal vowels, e.g. variations of ciążyć/ciężyć, as well as spontaneous nasalization, e.g. czestować > częstować.^[16]

The final vowel system was more or less similar to Modern Polish's vowel system.^[12]

Accent

Already in the 15th century one can find tendencies of fixing stress on the penultimate syllable, ultimately solidifying giving the modern Polish stress system. Between the 16th and 17th centuries, there was also a tendency to include enclitics in the stress pattern, e.g. bo'ję się, moż'na by, which did not continue.^[17] As this was happening, syncope occurred in words ending with -yja and -ija, exclusively Latin borrowings, where the -y- or -i- was dropped.^[18] Sometimes these forms can still be seen in liturgical songs or prayers, such as "Zdrowaś Maryjo".

Maryja > Maria

historyja > historia

Nouns

Masculine plurals are separated further by animacy, resulting in a more stable system of three levels of animacy, inanimate, animate, and virile. The biggest change was the separation of animate and virile. Before, one could see the virile plural psi (dogs), with psy being the animate plural. Nouns changed their level of animacy during this period to some degree, for example the animate nominative and accusative plural filozofy (philosophers) instead of the now nominative virile plural filozofowie and the genitive and accusative virile plural filozofów, ultimately settling in the 16th century.^[21]

This change ultimately affected the government of adjectives, verbs, pronouns, numerals, and participles, which all began to change their endings depending on the level animacy of the given noun.^[22]

For masculine nouns in the genitive singular we see wavering between -u and -a, which lasts to this day. Similarly, there is some shifting in the singular dative between -u and -owi, with -owi ultimately becoming more popular and -u being the dative singular only for a few nouns.^[23] In the plural, we see either -ów or -i/-y for nouns ending in -rz or -ż, which continues to this day.^[24]

The softening masculine singular locative ending -e after velars changes to -u, retained to this day.^[25]

człowiek > człowiece > człowieku

bóg > bodze > bogu

grzech > grzesze > grzechu

At the end of the 16th century we see a loss of the ending -i/-y for the instrumental plural and a generalization of the ending -mi as well as the proscribed -ami, used originally only for feminine nouns in the instrumental plural.^[22] Nowadays the endings -i/-y can only be seen in fossilized phrases such as "ostatnimi czasy" and "innymi słowy".

Masculine and neuter nouns also underwent a generalization, originally ending with the suffix -ech, or in the Lesser Poland dialect -och, now ending in -ách, which later changed to -ach.^[26]

Feminine nouns in the nominative originally sometimes ended in either -a for hard stems and -á for soft stems, with -á ultimately dying off either due to sound changes, analogy, or both. Nouns ending in the clear -a took -ę in the accusative singular whereas those ending in -á took -ą. When -á merged with -a, the two accusative endings were kept for a short time, but ultimately -ę became the standard ending due to analogy.^[27]

The original genitive ending for feminine soft stems was -e, changing to -i/-y. One could also sometimes find -ej for this declension, as well as for feminine dative soft stems, but this did not last.^[28]

Feminine nouns in the dative plural changed from -am/-ám to -om, matching the masculine and neuter dative plural ending. There are a few instances of masculine nouns taking the feminine -am/-ám endings, however, but they were rare.^[29]

Neuter nouns endings in pitched -é had a singular instrumental ending -im that later changed to -em.^[23]

Possessive pronouns and adjectives

In the 18th century the ending -ą for feminine singular accusative possessive pronouns began to supplant the ending -ę.

twoję > twoją

There was also variation in the masculine singular instrumental and locative ending in -emi and -ymi, which lasted even in the orthography until the orthographical reform of 1936.

nowemi > nowymi ^[24][30]

In the 16th century we see a replacement of -i/-y by -e for the masculine and accusative non-virile plural.

ty (from ten) słowa > te słowa

wszystki > wszystkie

Also in the 16th century we see -ej replace -e for feminine singular genitive.

sługa wieczne mądrości > sługa wiecznej mądrości^[31]

Verbs

The Middle Polish verb system doesn't differ too much from either the Old Polish or modern Polish verb system, however it is not identical. Some changes include:

1. A loss of the ending -ęcy as the active adjectival participle for feminine subjects, being replaced by -ący
2. A replacement of the old imperative ending -i/y with -ij/-yj or a null morpheme

zamkni > zamknij

zetrzy > zetrzyj

weźmi > weź

1. A loss of the analytical past as well as aorist in favor of the new morphemes. However, the aorist was kept in Silesian

robił jestem/robiłech > robiłem

1. The conditional mood, originally formed with the aorist endings, was replaced by forms from the Proto Slavic participles, influenced by their use as past tense forms.

bych > bym^[32]