Yleisen Kielitieteen Kurssi by Ferdinand de Saussure

A foundational work in structural linguistics that argues language is a system of signs made up of a signifier (sound-image) and a signified (concept), whose link is essentially arbitrary; it emphasizes that meanings arise from differences and relations within the linguistic system rather than from direct reference, distinguishes the social system of language (langue) from individual speech acts (parole), and promotes synchronic analysis of language structure alongside the study of historical (diachronic) change, laying groundwork for modern semiotics and structural theory.