Ferdinand de Saussure
Saussure was a professor in historical linguistics, which is concerned with how languages relate to each other and how they change over time. This interest in how language changes over time can be called diachrony. Saussure was more interested in synchrony, which doesn’t change over time. This means he looked at the parts of a language, as if they didn’t change. Saussure studied the structure of language without comparing it to other languages and without focusing on change.