Q: In a grammar book I noticed two or three forms of pronouns within one category (jego=go=niego in the genitive case). How can I tell which one to use?
A: These three forms, as well as two equivalent feminine forms (ją=nią), are used in relation to the words surrounding a particular pronoun and also the context. There are no strict rules as to which one to use in which occasion, but there are some hints you can use to decide. The shortest form in the masculine (go, mu) is used when the pronoun immediately follows a verb, such as in the example “Widziałem go” (I saw him), and not “Widziałem jego”. Pronouns starting with n- (niego, niej etc.) are used in connection with prepositions: “Idę do niego” and not “Idę do jego” (I’m going to him). In other cases, one may assume that “classic” forms (jego, jej, etc.) are the most suitable ones. Please note also that in pronunciation the shortest forms are not stressed, whereas the two syllable ones (jego, niego) are stressed.