Learn Croatian: Glazbenici sviraju svaki instrument s lakoćom. - The musicians play every instrument with ease.

When expressing the abstract manner in which an action is performed, Croatian uses the preposition s (with) followed by the instrumental case. Using the bare instrumental without s is typically reserved for the physical tools or means used to do an action (like writing with a pen or traveling by train).

Could I use sa lakoćom instead of s lakoćom?

In everyday speech, people sometimes use sa just for rhythm or flow. However, standard grammar dictates using the short form s unless the next word begins with a sibilant sound (s, š, z, ž) or certain heavy consonant clusters. Because lakoća starts with an l, the correct written form here is s.

Why doesn't svaki instrument change its ending if it is the direct object?

It is actually in the accusative case here because it is the direct object of the verb sviraju. However, for masculine nouns, the accusative case only takes a different ending if the noun is alive (animate). Since an instrument is inanimate, its accusative form looks exactly the same as its nominative form.

Why does the plural of glazbenik end in -ci?