In contrast to modern Slovak, the early Slovak language had three grammatical numbers inherited from Proto-Slavic, singular, plural and dual. Dual was probably never fully developed and was extinct already in the 14th century. Dual forms were recorded mostly in documents from Western and partially from Central Slovakia, but their usage in the 15th-16th centuries was limited to words that naturally come in pairs (ears, eyes, etc.) and words derived from the number two. However, they were already garbled or outnumbered by plural forms.