He was observant.
(1772 - 1829) A German poet, scholar, critic, novelist, playwright, and lecturer, he was one of the people who formulated the set of ideas that came to be called Romanticism.
He was also one of the first people to notice the systematic phonological relationship between deceased and living languages (e.g. words pronounced a certain way in an ancestor language will, based on an observed rule, be consistently pronounced in another way in a particular descendant language).
This observation was elaborated upon by Rasmus Rask, then Jacob Grimm, leading to the formulation of what was eventually called Grimm's Law, a set of rules that explains how pronunciation has evolved in Indo-European languages.