The Polish language started to change after the baptism of Poland, which caused an influx of Latin words, such as kościół "church", anioł "angel". Many of them were borrowed via Czech, which, too, influenced Polish in that era. Also, in later centuries, with the onset of cities founded on German law, Middle High German urban and legal words filtered into Old Polish. Around the 14th or 15th centuries the aorist and imperfect became obsolete. In the 15th century the dual fell into disuse except for a few fixed expressions. In relation to most other European languages, though, the differences between Old and Modern Polish are comparatively slight; the Polish language is somewhat conservative relative to other Slavic languages. That said, the relatively slight differences between Old and Modern Polish are unremarkable considering that the chronological stages of other European languages that Old Polish is contemporary with are generally not very different from the Modern stages and many of them already labelled "Early Modern"; Old Polish includes texts that were written as late as the Renaissance.
Spelling
The difficulty the medieval scribes had to face was attempting to codify the language was the inadequacy of the Latin alphabet to some sounds of the Polish language, for example cz, sz. Thus, Old Polish does not have a standard spelling. One letter could give several sounds - e.g. s can be read as s, sz or ś. Writing words was almost entirely consistent with the spelling of Latin, for example. Bichek - Byczek, Gneuos - Gniewosz etc.
Earliest written sentence
The Book of Henryków, contains the earliest known sentence written in the Polish language: Day, ut ia pobrusa, a ti poziwai, written around 1270. The medieval recorder of this phrase, the Cistercian monk Peter of the Henryków monastery, noted that "Hoc est in polonico".
Alphabet
Parkoszowic
About 1440 , a professor of Jagiellonian University, tried to codify the Polish alphabet. He wrote the first tract on Polish orthographic rules and rhyme Obiecado. The reform consisted in the introduction of round and unrounded letters on the distinction between hard and soft consonants. It also contained merging double vowels to a long vowel, for example: aa – /aː/. Parkoszowic's proposal was not adopted, and his theoretical concepts had no followers.
Phonetics
Over the centuries Old Polish pronunciation was subjected to numerous modifications. These are only the most basic ones. The consonant system transferred into the soft coronal consonants, for example for. Many consonant clusters were simplified; which in the process made assimilation reverse many consonants in words, before that following a voiceless consonant.
