Syntax rules determine whether a sentence is grammatically correct, and in linguistic analysis (parsing), understanding sentences involves breaking them into parts.

If you consider words of a language to be its signs, then its syntax is the set of rules which puts signs together to make statements, ask questions, and produce other utterances.

A study published in Nature Communications suggests that a small bird known the Japanese great tit uses grammatical rules in its calls. Until now, only humans seemed to use syntax this way.