Human language, the focus of linguistics, possesses unique characteristics differentiating it from other communication systems.  Nine key properties are highlighted:  sounds (primarily vocal, with speech preceding writing), systematicity (structured rules governing sound and word order), linearity (sequential arrangement of elements), arbitrariness (lack of inherent connection between form and meaning, though onomatopoeia is an exception), productivity (creative capacity for limitless new utterances), displacement (referencing things absent from the immediate context), duality (two levels of structure: meaningless sounds combining to form meaningful units), discreteness (distinct units of sound perceived as separate), and cultural transmission (language acquisition through learning, not genetics).  These properties contribute to language's flexibility and unique communicative power.