з + Instrumental (Accompaniment)

The construction з + Instrumental serves several specific functions:

• Accompaniment: Doing something together with another person or animal.
  Я йду з другом (I am going with a friend).
• Association/Ingredients/Features: Describing a physical feature, characteristic, or an added component.
  Кава з молоком (Coffee with milk), дівчина з блакитними очима (a girl with blue eyes).
• Manner: Describing how an action is performed.
  з повагою (with respect), з радістю (with joy).
• Interaction: Required by verbs denoting mutual action, especially reflexive verbs ending in -ся, such as бачитися з (to see each other with), сваритися з (to argue with), or домовитися з (to agree with), as well as verbs like розмовляти (to talk).
• Time / Progression: Describing changes over time.
  з часом (with time), з роками (over the years).

Euphony (Sound Harmony):
To keep the language melodic, the preposition changes based on the following sounds:
1. з: The mandatory form before words starting with a vowel (з Оленою, з апетитом), and often used as the default form before single consonants.
2. із: Used between consonants or before sibilants like с, з, ш, ч, щ, ц (із сестрою).
3. зі: Used before consonant clusters (зі псом), especially when the cluster begins with a sibilant or fricative like з, с, ш, щ, ч, or ц (зі студентами), and before the cluster мн- (зі мною).
4. зо: Used with numerals to mean 'approximately' or 'about' (e.g., зо два дні, зо три тижні). Note that in this specific usage, the noun is in the Accusative case, not the Instrumental. As a preposition of accompaniment, it is a rare alternative to зі before мною (зо мною), which is mostly poetic or dialectal, while зі мною is the overwhelming standard.

Note: The phrase зі Львова (from Lviv) perfectly follows these euphony rules, but note that it is an exception in terms of meaning and case, as it takes the Genitive case because з here means 'from'.

Refer to милозвучність в/у та з/із/зі for more details on these shifts.