Instrumental plural of nouns

In the last lesson you learned one plural ending that does two jobs: -ima / -ama is both the dative plural (to the friends) and the locative plural (about the friends, in the cities). Here is the good news: the third plural case you need, the instrumental, uses exactly the same form. There is nothing new to memorise about the ending. What is new is a third job for it — and learning to tell the three jobs apart.

Same form, third job

In the singular you already use the instrumental for two things (A1 lesson 30): with whom you do something, marked by the preposition sa (or s), and by what means you do it, with no preposition at all: sa bratom (with my brother), vozom (by train). The plural works the same way, and the form is the -ima/-ama form you already produce.

As in the last lesson, a masculine stem ending in -k softens to -c before -ima: putnik → putnicima, drug → drugovima (the short masculines keep their extra -ov-/-ev- syllable in every plural case). Note the neuter kola (car) and vrata (door): they only exist in the plural, so kolima is how you say by car.

sa for company, nothing for means

• Company — sa + instrumental. Who is with you: Putujem sa prijateljima. (I am travelling with friends.) Idemo na aerodrom sa drugaricama. (We are going to the airport with friends.)
• Means — bare instrumental, no preposition. What you use to get there: Na more idemo kolima. (We go to the seaside by car.) Ljudi idu na posao autobusima i tramvajima. (People go to work by bus and tram.)

Never put sa in front of the vehicle you travel by. Idemo kolima, putujemo vozovima — no preposition. Idemo sa kolima sounds as if the car were your travelling companion, and Serbian speakers hear it as a mistake. (Sa is fine when the vehicle is not what carries you: problem sa vratima, a problem with the doors; čekaju nas sa kolima, they are waiting for us with the car.) The rule of thumb: if the English has with, use sa; if the English has by, use nothing.

The bare instrumental plural has one more everyday use with time words: it says for days / nights / hours on end. Vozači kamiona voze noćima. (Truck drivers drive for nights on end.) Putujemo danima. (We have been travelling for days.) Notice noćima, from the i-type feminine noć — it takes -ima like a masculine, not -ama.

One form, three readings

Because the ending is shared, you cannot tell the case from the ending alone. Read the sentence around it: a recipient is dative, a place or topic after u, na, o is locative, sa or by what means is instrumental.

The form learners still get wrong at this point is the i-type feminine: stvar, noć, reč look like masculines and behave like them here — stvarima, noćima, rečima, never stvarama. Only feminines that end in -a in the nominative take -ama.