More specifically, it is a member of the Lechitic branch of the West Slavic languages, along with other languages spoken in areas within or close to the area of modern Poland: including Kashubian, Silesian, and the extinct Slovincian and Polabian.
It now depends on the gender of a noun (smok, o smoku – foka, o foce) (a dragon, about a dragon – a seal, about a seal) and to some extent on the hardness of a noun's stem (liść, liście – list, listy) (leaf – leaves, letter – letters).
The reason for this last change was most probably the free word order and the ambiguity that it could entail in phrases such as syn kocha ojciec (a son /nom./ loves a father /nom./) and ojciec kocha syn (a father /nom./ loves a son /nom./).
The accusative was the same as the nominative until the 14th–15th century (in the region of Mazowsze until the 16th century), and nowadays this feature is preserved in common phrases such as iść za mąż (to get married), siąść na koń (to mount a horse), na miły Bóg (dear Lord!
Until the 15th–16th century it was also applied to masculine and feminine nouns ending in -k, -g, -ch: Bodze (god), gresze (sin), mlece (milk).
Nowadays it is present in forms such as Boże, człowiecze, Kozacze (also człowieku, Kozaku), and also księże, additionally after -ec: ojcze, starcze(father, old man) (connected with the third palatalization).
Forms Włoszy, mniszy (Italians, monks) have been replaced by Włosi, mnisi with the phonetic softness introduced in the 17th century.
The ending -e, derived from the stems ending in -i- (gost-ьje, lud-ьje) (guests, people), -n- (dьn-e, kamen-e, mestjan-e) (days, stones, townsmen) and forms such as przyjaciele, cesarze (friends, caesars), have dominated soft-stem masculine nouns.
Since the 16th century it has been gradually disappearing, especially from inanimate nouns and those referring to nonpersons, still Norwid (1821–1883) used obłokowie (clouds) to make up a rhyme.
Due to the influence of the Latin language, it has been applied since the 15th century to the stems of male nouns borrowed from Latin and German: akta, fundamenta, grunta, (files, foundations, grounds) and temporarily also to originally Polish nouns: okręta, pociska (ships, bullets).
Nowadays, applying the ending -a to the stems of masculine nouns is generally not possible, however: akta (files)||akty (acts).
Initially, these forms were interpreted as collective nouns (bracia stała = braty stały) (brothers stood), księża poszła = księdzowie poszli (priests went), and were declined in the same way as female nouns (others of this type in the accusative had applied the ending -ą, in the genitive, dative and locative: -ej).
In the writings of Skarga (1536–1612) they were declined in the same way as plural nouns (braciom, braćmi, braciach, księżom, księżmi, księżach) (brothers, priests).
In dialect forms such as swaciå, muzykanciå, adwokaciå (matchmakers, musicians, lawyers)can be found.
Until the 17th century, its traces were present in the old masculine stems ending in -o-, -jo-: genitive woz (carriage), god, tysiąc (thousand), dziej, włos (hair).
In Old Polish it had a slightly different pronunciation and was more widely applied: pisarzow (of writers), koniow (of horses), dniow (of days), miesiącow (of months), in dialects: krolew (of kings).
Old accusative was and still is used for stylistic reasons: króle (kings), pany (masters), chłopy (peasants).
In principle, today it is only applied to the stems of masculine and feminine nouns in the nominative ending with −0 and having a phonetically soft-stem.
The ending -oma, derived from the dual number, was applied to the stems of masculine nouns in the 16th–17th century.
The ending -'ech was applied in the Old Polish to masculine and neuter nouns, especially those with hard-stem: wilcech (wolf), syniech (son), skrzydlech (wings), leciech.
The mixed declension is characteristic of forms such as poeta (poet), mężczyzna (man), Jagiełło, Fredro, sędzia (judge).
In Old Polish forms such as starosta (prefect), poeta (poet) were declined like feminine nouns.
In the 15th century nouns such as sędzia < sądьja (judge) were given in singular genitive, dative and accusative forms like adjectives.
They have undergone just slight changes: The old genitive čьso was transferred to the accusative and has spread to be applied to the nominative.
The old accusative has preserved its prepositions: w niwecz < vъ nivъčь, przecz < prěčь, zacz < začь.
The forms of collective numerals have been blended (portmanteau) The dual as a productive category has disappeared.
The ending -i disappeared (at first from endings *-cy < -ci): It has undergone just slight changes: Many verbs changed their present tense forms by analogy: Instead of -ętъ for athematic verbs or for verbs with stems ending in -i-, the form -jątъ is used: Based on the conjugation of athematic verbs, the new conjugation -am, -asz was introduced in verbs where contraction resulted in a long vowel in the ending (very rarely -em, -esz): The 1st person singular changed by analogy to the athematic conjugation e.g. dam ("I will give"): In the 3rd person plural the original vowel sequence remained uncontracted (compare athematic dadzą "they will give"): The aorist and imperfect tenses inherited from Proto-Slavic disappeared.
Only the first person singular ending of the aorist was retained in some dialects: byłech, byłek (= byłem) ("I was").
The aorist of być ("to be") was retained to form the conditional mood, was changed by analogy to the past tense and was subsequently reanalyzed as a particle.
The Proto-Slavic conditional form was replaced by an analitical construction composed of the aorist of the verb być ("to be") and the old L-participle.