Personal pronouns in oblique cases

Czech personal pronouns decline to reflect their role in a sentence. For singular pronouns (já, ty, on, ono) and the reflexive se, the system features a "doublet" system (plural pronouns like my, vy, oni and the feminine singular ona do not have these doublets):

• Short forms (clitics): Words like mi (to me), ti (to you), mu (to him), tě (you), and ho (him). These are unstressed and must occupy the strict second position of a clause. True clitics (like mi, ti, mu, tě, ho, se, si) cannot be the first word or phrase of a clause, as they must occupy the second syntactic position, and they can never follow a preposition. For example, the Dative clitic mi cannot follow a preposition; you must use the long form mně. (Note: The 1st-person singular pronoun mě is technically a short form, but in modern Czech it has generalized to be used in all positions for the Genitive and Accusative cases, including after prepositions, effectively replacing the historical long form mne in everyday/standard usage, e.g., beze mě).
• Long forms: Words like mně, tebe, and jeho. These are standalone, stressed words used at the start of a clause, for contrastive emphasis (e.g., "I saw YOU, not him"), or after prepositions.

Reflexive Pronouns:
The reflexive pronouns follow the exact same doublet system and second-position rules, with short forms se and si, and long forms sebe and sobě.

The N-Prefix Rule:
When a third-person pronoun (he, she, it, they) directly follows a preposition, it generally gains an initial n-. For example, jeho becomes něho, jí becomes ní, and the masculine accusative jej becomes něj (for inanimate) or něj/něho (for animate). Similarly, the feminine accusative ji becomes ni (e.g., pro ni). The common masculine and neuter short form ho (used for both Genitive and Accusative) cannot follow a preposition at all. In the Accusative, it becomes něj or něho (for animate masculine nouns), něj (for inanimate masculine nouns), or ně/něj (for neuter nouns). Additionally, for inanimate masculine and neuter nouns in the Accusative, an optional but common -ň contraction can attach to short prepositions (e.g., pro něj becomes proň, na něj becomes naň). In the Genitive, it becomes něho or něj (e.g., bez něj). In the Dative, jemu becomes němu (e.g., k němu). For the plural "they", the forms also take an n-: jich becomes nich, jim becomes nim, je becomes ně, and jimi becomes nimi. Note that because the Locative case always requires a preposition, its forms (něm, ní, nich) only exist with the n- prefix. Note: This rule applies to third-person personal pronouns and the formal relative pronoun jenž. First and second-person pronouns never take an n- (it is na mě, never na ně when meaning "onto me"). Crucially, this applies to personal pronouns, not possessive pronouns (compare bez něho with bez jeho bratra). Many secondary prepositions (such as díky, během, pomocí, vůči) often take forms without the n- prefix (e.g., díky nim or díky jim).

Preposition Vocalization & the Instrumental Case:
When using the first-person pronoun after single-consonant prepositions or specific primary prepositions ending in a consonant (such as bez, od, nad, pod, před, přes), the preposition must vocalize (add an -e) for easier pronunciation. For example, k becomes ke mně, v becomes ve mně, bez becomes beze mě, and od becomes ode mě (but secondary prepositions like kolem do not vocalize: kolem mě). In the Instrumental case (7th case), the pronoun form is mnou, and the preposition s vocalizes to se mnou (with me), just as nad becomes nade mnou. Other important Instrumental forms include s tebou (with you), s ním (with him/it), and s ní (with her). Explicitly, the bare forms jím and jí become ním and ní after prepositions.

Feminine Pronouns Ji vs. Jí:
A common challenge is distinguishing the vowel length in the 3rd-person feminine pronoun. Use the short ji for the Accusative (4th case, direct object). Use the long jí (or ní after prepositions) for the Dative, Locative, and Instrumental cases (3rd, 6th, and 7th cases). Since the Locative case always requires a preposition, it will always appear as ní.

Spelling Mě vs. Mně:
Native speakers often confuse mě and mně because they are pronounced identically [mňe]. The rule is: mě is used for Genitive and Accusative, while mně is used for Locative and as the stressed/prepositional form for Dative (the unstressed Dative short form is mi). A helpful trick is to substitute "you": if you would use tě/tebe, write mě; if you would use tobě, write mně. Note that in formal or literary contexts, you might also see mne used instead of mě for Genitive and Accusative.