са / с + Instrumental

When describing companionship, partnership, or mutual interaction, Serbian uses the sociative construction: с / са + инструментал.

1. Choosing Between 'с' and 'са':
The base, primary standard form is с. The extended variant са adds a vocalic ending to ensure smooth pronunciation under specific phonetic conditions:

• Obligatory са: Must be used before words starting with sibilant fricatives (струјни сугласници: с, з, ш, ж, e.g., са сестром, са Жељком). Crucially, affricates do not trigger са; words beginning with ц, ч, ћ, џ, ђ take regular с (e.g., с царем, с човеком, с ћерком).
• Obligatory са: Must be used before consonant clusters where the second sound is a sibilant fricative (e.g., са псом, са Ксенијом).
• Obligatory са: Must be used with the 1st person singular instrumental pronoun: strictly са мном ('with me'). Note that the lengthened form мноме is used for the bare instrumental (e.g., поноси се мноме), never after са.
• Usage before other sounds: Standard normative references consider с the primary base form and standardly recommend it before vowels to prevent hiatus (e.g., с оцем, с омладином), as well as before ordinary consonants (e.g., с дедом, с мајком, с братом, с пријатељима). However, standard authorities (including the Pravopis) note that choosing са in free syntactic combinations is a legitimate stylistic and euphonic option in standard Serbian—especially for sentence rhythm or when another sibilant occurs nearby in the word (e.g., са испитом, са осам)—rather than a mere colloquial error.

2. Company vs. Means (Crucial Distinction):
In English, 'with' translates both accompaniment ('with my friend') and instruments ('with a pencil', 'by bus'). In Serbian, these are completely separate structures:

• Accompaniment & Accompanying Features = с / са + инструментал (Пијем кафу са сестром — 'I drink coffee with my sister'). While primarily used for living companions, с / са also appears with inanimate nouns to describe accompanying ingredients, attributes, or manner (e.g., кафа са млеком — 'coffee with milk', стан са терасом — 'an apartment with a terrace', са задовољством — 'with pleasure').
• Instrument or Means (with a tool / by transport) = bare instrumental without с / са (Пишем оловком, Путујем возом). Saying *идем са возом sounds humorously as if the train is walking beside you!

3. Spelling Rules:
Never write an apostrophe after с (writing *с' is incorrect). Additionally, са мном is always spelled as two separate words, never written together.